I don't know what it is either but some people have refactor itch and others don't.

Making code changes means one takes on the risk of breaking things. I think the people who don't break stuff are the ones who continue to refactor. The ones who don't either are scared of breaking stuff or had a bad experience with breaking stuff.

I suspect the people who refactor have what can be describe as perfectionism or obsessive compulsive.

I'm in that bucket. I can see certain code which is too complex or didn't handle a requirement well and I want to get it to be stated more simply.