That's mostly because people more so care about the characters in a singular manner, who are they as a character, rather than what company they come from. Capcom's a great example of this. RE gets spirits, but DMC fans would still want Dante, AA fans with Phoenix, Okami fans with Ammy, even me with another Mega Man(though obviously not this pass). People don't want Dante because he's Capcom, but because he's Dante.
But since Capcom as a whole isn't for this particular spot, so these leakers are kind of killing the hype of guessing who it is, but not having the stones to just outright say it. Same for Namco and whoever else. The representation between characters from third party companies and series is already un-even, so why should it matter now? Castlevania and Street Fighter get two characters, would it be nice if Sonic and Mega Man did as well? Of course it would, but it's not like it has to be done just so Thanos doesn't flip his ****.
Heck, even with Joker, most of that dealing was Atlus rather than the main branch of SEGA.