Not all refactoring fit neatly alongside existing work.

Sometimes you get a small change request that suggests a broader refactoring. You're pretty sure it will be valuable in future, but it would be a lot more work and isn't that useful in the short term. So if you try and do that refactoring upfront, you get pushback for wasting time on a small change. And then again on the next relevant change.

Developers often want to schedule these kinds of refactorings, because otherwise they get pushback on every chance they might otherwise have to fix these problems.