It's a bit of both. Some of the developers I work with could find plenty of time to write better code if they cared to. It would save many hours of debugging or rewriting that we always have to do down the line, sometimes even mere months after the original code is written.

The "bad legacy code" excuse is often true, but in my experience the same devs who wrote "bad legacy code" 5+ years ago are still writing bad legacy code right now (or to put it better, it will become bad legacy code soon). My personal achievement is that I started to get ahead of it now and get to make a change for the better before it "settles" down and continues to haunt us in future. I think at some point, as you get older, you just stop giving a fuck since there's always the next generation that gets hired, full of zeal and enthusiasm, that will inevitably fix it. And some people probably just do it for job security.