Many companies have tons of desginers who need to prove they are needed, so they force change for the sake of change - at the cost of users.
That may be one part.
But another part is companies that need to demonstrate to their uses that a version change is a big change.
Microsoft is (im)famous for this: as far as I can tell, there has been little need for the constant UI churn in windows aside from convincing users that a new version is big enough to warrant that appellation (as opposed to a service pack/patch).
So I don't know where this conspiracy theory comes from, but it's entirely unfounded unless you're talking about a designer like Jony Ive with the power to go through multiple obstacles with ease, in which case the change isn't happening to prove he's needed but because he has a different vision.
Definitely not the case everywhere.