I believe it's because designers in large corporations feel the need to continuously justify their own employment and their salaries. So things change not because users request them, but because someone somewhere has to justify being a lead UI designer and their $$$ salary - and nonsense like moving the start menu to the middle ends up being "their thing" purely because they had the mental strength to push it through endless meetings and reviews and someone finally said fine ok we'll do this.

I see the same thing literally all the time with Google products, every revision of YouTube/Google photos/drive/android/Gmail just shuffles thing around without any obvious reasoning behind it, it's just "well, time for a new update, let's move things around again".

there is also a lot of bikeshedding around design at the management and executive level, and it is constant. ("Can we make it pop?", "It just doesn't feel right", "but the iPhone does it this way," etc.)

At least looking at people I've worked with in design, fighting your client constantly is not a good idea if you want to have a roof over your head. They'll just find someone willing to say yes.

It's become so annoying I dread weekly sync-ups now. It feels like an hour-long UI QA session.

The sad part is that those hothead UX designers could be earning their keep if they figured out a way to have some radical UI while maintaining concurrency with a historic UI that could be switched by the user.

Designers at the corporate level with the power of, say, Jony Ive at Apple are extremely rare.

From working with designers and in frontend, it is probably management or executive level keeping up with the Joneses.

This drives me absolutely nuts too. There is just too much pressure from various different job functions within companies to constantly change things even if it doesn't actually improve the customer's experience. People don't want to maintain old products, they want to work on something new. Compensation and promotions are dependent on shipping a fancy new product (looking at you Google). Management pressures people below them to change something even though they don't understand the customer's needs. I'm sure you could come up with a dozen more reasons.

This has gotten so much worse now that everything is a subscription web service and you can't continue using the product unless you accept whatever crappy redesign they have pushed out this time that took away the feature you liked using or the workflow you are used to.