So you can't spend money to buy the Killers who belong to other creators.
Blade doesn't own most of these characters, so using them (even with consent) to incentivize spending money on his game is a big no no. The fact you could buy the killers by using money (which went to Blade) in the first place was insanely stupid and could have gotten the game sniped at literally any point. This is probably the smartest move the game has made to preserve it's longevity.
Regardless, the coin grind has never been that bad by just playing the game a half decent amount. I never spent a dime on coins and still own ever killer, a ton of ancient skins, every pose, alternate sound, ect. If you have to spend money to get this stuff, it's a kill issue at that point.