Because there is a lot in these two trailers playing heavily to males and females. Successfully in my opinion.
The "ugly duckling" story with Chris Evans as the little guy trying to prove he has it in himself when nobody else is ready and willing to believe in him. That's a universal theme and taking one look at him all meek and lowered begging, "Just give me a chance..." will seal the deal with women, who do matter to the success or failure of these big releases contrary to the belief of fandom.
Setting it in WWII, making the primary villains as the Nazis (another universal theme that made Inglorious Basterds a big hit) and going for a full-on retro-era epic adventure with superheros will get the men.
But ultimately...I'd say it comes down to this.
People are ready to pump their fists in the air and scream, "YA! USA!" while waving the American flag in a way we haven't seen onscreen in...years. Sam Raimi took advantage of that in his three Spider-Man films by doing that to great success and applause from audiences and as much as I loved Superman Returns, they were foolish to not embrace the American nature of the character and myth. I seriously doubt we get that in The Man of Steel either.