That's not true. Lois has a personality.
Steve is probably the weakest part of the Wonder Woman mythos, which is funny because he's kind of what initiates the plot at first. It's kind of like Krypton exploding being the weakest part os the Superman mythos, or that guy killing Bruce's parents being the weakest part of the Batman mythos. I guess it kind of makes sense because Superman never had an explosion for a supporting character. And if Joe Chill was hanging out in the bat cave all the time it would be a little depressing and awkward.
Anyway my point is that Steve isn't a very interesting character and besides being the impetus for Diana to leave the island and for Hippolyta to want to have an ambassador to man's world, he really doesn't have anything to do with any of the major plots or story lines in Wonder Woman's comics or any of the things that make her interesting. I mean, back when the comic was set in World War Two and the bad guys were mostly Nazis, it kind of made sense because he was an Airforce pilot but somehow also an OSS agent.
I guess he needed more hours at work to pay for a car or something.
But all of the things that have really come to define Wonder Woman over the years, the stuff that actually makes her cool and interesting, Steve doesn't really fit into. Greek mythology, international politics, the weird incest-y family dynamics of the Greek Gods, being a role model and religious figure, decapitating ugly lizard women, mommy issues, overt paganism, implied bisexuality, Maxwell Lord killing, giving Superman relationship advice, sexual tension with Batman, Steve Trevor just doesn't really fit in with any of that stuff by the nature of his character. He's a military guy. He flies planes and kills whoever America doesn't like right now. It's kind of hard to find not stupid reasons for him to be involved with stuff that doesn't have anything to do with war or protecting American interests.
And on top of that, he and Diana don't make a very good couple. That's partly because the writers never gave him any kind of personality besides being generically nice and brave and patriotic, but that's also because he and Diana never had any chemistry.
Clark Kent and Lois Lane have loads of chemistry. They have a lot of differences so it's not like they're just dating clones of each other. Clark's from a small town and Lois is from the big city, Clark is really polite and quiet and Lois is really blunt and sarcastic, Clark always has to hide something about himself and live this dual life and is never totally honest in any circumstances while Lois is really open and self confident and honest and values truth and honesty a lot, Clark's a very private person and respects the privacy of others while Lois isn't and doesn't, Clark is really optimistic while Lois is really cynical. But at the same time they have some really important things in common. They both want to help people, they want to make the world a better place, they want to make sure bad people don't get away with doing bad things and ordinary people don't get stepped on and are given a chance, they're both very brave and selfless, and most importantly they both see something that they need in each other. Lois grounds Clark, she's a really normal person with normal concerns and problems, and that sense of normalcy is why he has a secret identity in the first place. Clark, as Superman, represents all this optimistic ideas Lois gave up on a long time ago, but the fact that he chooses to live a normal life and be a normal man as much as he can grounds that optimism and makes it real for her. They're just two people who fit together really well, and it makes sense that they'd fall in love and care about each other very deeply.
Steve and Diana don't have that. Again, that's partly because Steve basically doesn't have a personality, but it's also because of how Diana's written. Wonder Woman was designed to be a strong, independent person to shake of negative gender stereotypes. Now I'm not saying that a woman isn't strong or independent if she falls in love with a man, because that's dumb, but what I am saying is that she is, partly by design, a character who doesn't have romance as a goal and who's independence is actually a key part of the story. Her origin story is her gaining independence from her mother and going pout into the world on her own all coming-of-age style.
It also doesn't help that Steve and Diana aren't equals in the story. The first published Superman story was told largely from Lois' point of view. Superman's the title character but Clark and Lois are really both the protagonists of the story, something a lot of writers forget because they're dumb.
That's not the case in Wonder Woman. Steve arriving on the Island sets the story in motion, but after that it is very much Diana's story. It's her defying her mother and leaving for man's world, it's her becoming her people's ambassador, it's her becoming a hero and finding a sense of purpose in life, it's her dealing with the challenges that come at the price of her independence, and Steve really doesn't have much to do with any of that. He just stands around and occasionally shoots someone. He does not share the role of protagonist with Diana, he is very much a supporting character, and when the big focus of your story is the main character gaining independence for the first time in her life, it's really hard to put her into a relationship with an underdeveloped supporting character with no bearing on the plot after the first issue and have it ring true.
I kind of think that Steve would work better as a villain. Like, not a super evil arch villain, but as an antagonist who's not a bad person but who's on a side that stands in opposition to the hero.
What I mean is, Diana's an ambassador to man's world, and that means she's going to have to deal with a lot of political ********, especially from the United States and the other G8 and NATO nations. Now, Diana's all about peace and truth and mercy and helping the helpless and tempering actions with wisdom. Not that she's not a warrior because she totally is, and I still think her being the member of the Trinity who's most okay with killing guys makes a lot of sense. But her patron god is Athena, who's the god of war and wisdom. She fights, but she still tries to not kill people if she doesn't have to and she tries to avoid fighting if she can. And she only fights as a means to help people who are in trouble. So she'd stand in opposition to a lot of stuff America does, like our foreign military presence, how we treat poor people, how we treat not-white people, how we treat gay people, basically how we treat people who don't look and act like your average host of the 700 Club, and the fact that she's such a huge feminist icon and a religious figure to some means that her badmouthing them actually would hurt them a little bit. In addition to that, she's into a lot of stuff that's not cool with most modern day Americans. She's bisexual, she's foreign, she's royalty, she's a pagan, she's into bondage even though they don't talk about that much anymore. Both socially a politically, she'd be considered "un-American" by a lot of people in power.
And you've got Steve, who's a soldier, and a patriot. It would make a lot of sense to have his appearing on the Island what gets the ball rolling, and he starts off as Diana's friend, but then as Wonder Woman starts making waves and seems like she might be a threat to political stability, Steve starts getting orders to spy on her and assess her weaknesses and make plans to be used against her, and he's all morally conflicted about it but goes ahead anyway. Then you'd have this issue of wether or not they can trust each other, and you can keep bringing Steve back because he's had firsthand experience with all the weird magical stuff Wonder Woman deals with because they used to hang out, and it would make interesting conflict and give him something to do and a reason to be there and some actual character development.
But I don't know that's just what I think.