Unless management has made the decision to invest in a solid-wall backstop of functional tests, then no amount of great programmers can clean up a codebase. I've known and learned from some of the best coders alive, and none of them would wade into a known-good codebase that they didn't have solid experience with or responsibility for and start refactoring. Code that they were on the hook for? Open season. Code that someone else was going to get the call on at 3 a.m.? Wouldn't touch it with a ten-foot pole.
Given that, I wouldn't expect '50% of any companies' to be good. "If it ain't broke..." is really good advice about 95% of the time. If you're 50-100% overbooked, you don't screw with other peoples' code just to try to make things better around the office.