Software is a kind of art. It's never finished, but abandoned. You can continue to polish the code without adding functions (or even fixing bugs), so yes, it can take forever.

OTOH, when you give that ~180%, you reach to a maturity level most of your users perceive as "done", so what's most developers are after is that point.

Then, there are passion projects, which go on for 30+ years (Vim, BBEdit, etc.), where people work on it because they love the project and they're able to.

*: BBEdit is closed source/commercial software, but it sells because it's well crafted. It's not crafted to sell well.