I doubt it's any kind of directive from Leob. It's more of a series-by-series/character-by-character decision, I definitely feel it's up to the show runner. There are a bunch of costumes throughout the all series but the focus is more on story and function rather than obligation. Cloak and Dagger aside since I haven't seen it, all most of the series without outfits makes sense and even when they have outfits but don't wear them it's an organic part of the story. I remember when the first Defenders trailer came out so many people on this bored claimed they were doing away with the red costume but there was a perfectly valid and logical story reason for when he wears the outfit, specially in a world where real costumed superheroes is a relatively new and rare concept.
Personally, I much prefer this approach. I like when writer focuses more on a character's personality, goals, and motivation rather than superficial fan service that can hurt the story. Kind of like what vulture said in Homecoming "what is this pro-wrestling" because even the films introduce outfits in a very organic way, there's very few masked individuals who have colorful outfits for no reason.
Luke Cage did a great job having villain names be introduced as nicknames most of the character got growing up. Daredevil did a great job building up to the red suit in a very consistent and logical manner that only helps the story.
The only show that I felt didn't do a good job was Iron Fist. Not that the lack of the costume wasn't organic or consistent, but because the show had no real visual identity like the others to make up for it. Plus the story we got could have really used an overhaul, one that would make the costume an organic part of the story. That being said Defenders have the perfect tee up for Danny to become a mask vigilante and if season 2 doesn't take advantage of that it would be a huge misstep.
Wouldn't take that much work, Danny is already operating as a vigilante just have one criminal recognize him and attempts to sue Rand Industries. Then have Ward tell Danny off for being irresponsible, have Melvin Potter fail to get a pitch for his armor, Danny takes pity and when talking to him notices it's that same material as Daredevil, convince Ward to hear him out, then Danny has Potter make him an outfit. Then boom, you can have a costume as early as episode 3.
I don't feel this whole "Marvel TV hates costumes" holds much water and I wouldn't be surprised if people start saying the same thing When the DD season 3 trailer drops and we don't see the red costume because off plot related reasons.
