The really cool thing is that eventually you're able to deliver large, complex tasks in very brief times and then spring on the PM/management that you're able to do this _because_ you've been refactoring. That's made a believer out of at least one of my PMs.
Obviously this doesn't work in all circumstances - it's not always feasible to get the really systemic, contagious debt cleaned up as part of feature work, and if the PM catches on then it makes this tactic difficult to continue.
The bigger obstacle I've had, though, is other developers who haven't fully bought into a culture of continuous improvement. Fear of breakages causes refactor paralysis, which makes it easier to break things when working on them, which increases fear, and so forth. I'm not really sure the best way to deal with that aside from adding a bunch of unit tests (which I still sometimes get pushback on)