The "tech progressive" mindset cannot comprehend the idea that something cannot be improved or shouldn't be "enhanced". It is too close to the abyss.
Also, don't want to overlook the fact that people have to justify their jobs. If you are employed as a designer, and you were to tell your employer that The app is in good shape and doesn't need any design work, you are putting yourself out of a job. Now scale that up to an entire team of designers, or even a department with a chief designer, and you have a bunch of people. Primary incentive is to continually change things. I don't think it's a coincidence that bigger apps from companies that are big enough to hire Full-Time designers are constantly churning their UI.
I don't mean this against designer specifically. I've seen plenty of software engineers that do the same thing. Hell, I've caught myself doing the same thing. It's just part of being human, but recognizing our human nature and not doing dumb things because of it is an ideal to shoot for in my opinion.