Because he’s an extreme perfectionist, and it will never be perfect.

There’s a GREAT book about the making of different games called Blood, Sweat, and Pixels and it includes a chapter on Stardew Valley. Pretty much the only reason Stardew was released was because Ape had pretty bad financial troubles. He won’t be in that situation again thanks to Stardew’s success.

HC will never be good enough (in Ape’s super-perfectionist mind), so he’ll keep working on it forever. And he won’t bring anyone in to help him finish it for the same reason. I mean, we’re already six years into development and he still hasn’t indicated anything about being remotely close, or even said “I want to finish these things before I release v1.” He wants to release a perfect game that does everything he could dream of as v1, and doesn’t want to compromise with anything less.

It’s basically a curse of his and TBH I feel bad for the guy. Do read the book (or at least the Stardew vignette) if you’re a fan of his work - it was very enlightening.