Not based on anything I can verify, but my feeling is that when a company gets to a certain size and becomes high profile, it will attract certain types of employees as well. The more high profile, the more a UI/UX department will want to put their stamp on it. Instead of looking at what would make the product more user friendly and accessible, they'll be attracted to the shiny new things that they can do, simply because they can. The little nuances that are present in the old are allowed to fester until all of them combined lead to a general view that the whole thing is crap. Instead of doing small incremental improvements, they'll convince everybody (up to c-level) that a complete overhaul is the only way to move forward. This usually tends to happen in an echo chamber, where everybody who doesn't have the same vision of grandeur is excluded as part of the conversation. That, combined with business goals around profitability, is a dangerous thing to happen, and from my experience usually ends up in tears.

But hey, I like boring things ;-)