Of course they can, ultimately everything is up to them.
Can they cross promote? Yep,Through the various CW shows. Heavily requested falls into that "known name" popularity area. I can say mirror master was requested a lot but not as heavily as others. Terra/Starfire were and Teen Titans: The Judas Contract comes out soon so request and promotion there. It's not about having a certain amount of Batman characters so they should cut some, it's about having representation of other series and if you're looking at who to cut the guy with 8 names on the roster should be looked at before Lex Luthor.
The millions of casuals that will play this game want Superman, Batman, WoWo, GL, Flash, Aquaman, Joker, Harley Quinn, Robin. That's who appeals to casuals the most, Ivy/Scarecrow is just icing. Those 10 characters are the vast majority of your sales right there. Those millions may not want Circe/MM over CW/Bane but they got who they actually want regardless of if those two get cut or not and you've already locked down a large portion of your sales with them.
"Most probably don't know who they are".
How are people gonna learn if you don't put them in anything? Casuals interested in Injustice 2 that never heard of Swamp Thing are gonna learn some stuff about Swamp Thing and can become a fan. My brother became a fan of Grundy through IGAU. Never heard of him before that game.
I care. As a hardcore DC fan I care a lot. Here's the Breakdown of characters (not including skins).
Superman: Superman, Brainiac, Supergirl.
Batman: Batman, Robin, Joker, Quinn, Ivy, Scarecrow, Bane, Catwoman.
Wonder Woman: Wonder Woman, Cheetah
Flash: Flash, Grodd, Captain Cold
Green Lantern: Green Lantern, Atrocitus
Green Arrow: Green Arrow, Black Canary
Miscellaneous: Swamp Thing, Blue Beetle, Cyborg, Aquaman, Black Adam, Firestorm, Dr. Fate, Deadshot.
Batman is tied with people that have one representative. His list ties the entirety of the miscellaneous list. Tone it down.