So we're looking at a cheap ripoff of the characters either way. Why bother using the MCU at all then? Why not use Marvel cartoons? Why does it have to be awkward uncanny valley Chris Pratt voiced by some charmless anime dork?
Same as any other world, because the developers of the game like the franchise and pushed for its inclusion or thought it would make for a good addition. Also the whole thing is kind of a trend-setter in cinema with a likely high in interest coming later this year as the old guard starts passing the baton, so that helps.
Who would you suggest is a villain that would actually be worth including in a Kingdom Hearts world? Keep in mind that their actor is likely either too expensive or too busy to reprise the role. You think Malekith is worth it? How about the oh-so-charismatic and well-written Ronan the Accuser?
You say that like Disney villains haven't been treated like jokes after the first game, like how they turned Maleficent into a weird Team Rocket-esque figure or stuff like this:
The average Marvel villain would fit right in.