I don't know about anybody else, but I know I have a huge motivation cliff when it comes to continuing to pay the consequences for old mistakes that I have already sacrificed to make amends for?
How do I sell my coworkers on making a change that's the Right Thing to Do when we all know damned well that we're still going to have to support the Wrong Way for another four years? I might as well grow thick callouses, learn to Embrace the Suck, or self-select out of this project.
If we could make such large changes while preserving the old behavior, I think we'd get away with it, but there are limits to how much you can refactor, and people like to hitch their agenda to something with momentum, like a rider on the Farm Bill, and the architects of the change might have ulterior motives of their own.