It's a general curse of anything that becomes successful at a BigCorp.

The engineers who build the early versions were folks at the top of their field, and compensated accordingly. Those folks have long since moved on, and the whole thing is maintained by a mix of newcomers and whichever old hands didn't manage to promote out, while the PMs shuffle the UX to justify everyones salary...

im not even sure id say they were "top", id more just say its a different type of engineer, that either doesnt get promoted to a big impact role at a place like microsoft, or leaves on their own.