I do enjoy cleaning code a lot.

When I work on shitty code I'm always thinking about how shitty it is and thinking on how a different design would make it much easier.

When you clean the code, you're implementing that perfect design you were thinking of all that time. And you know from that point on you'll be thinking less about how shitty the code is.

If your only task is to clean code and you're not gonna work on that codebase afterwards, it's not as rewarding though.