Why doesn't IK just fix everything? I thought IK was the silver bullet that just made everything possible.

Well, I mean, it does, but IK will allow you to move things like final positions of hands and feet, but it won't allow you to make them not look ridiculous, right? So if it's a small nudge, sure, that'll totally work. But if you want to move the character, say, half a meter or something like that, there's just absolutely no way we can do that without completely reworking the cockpit.