Speaking entirely out of my ass here:

FOMO for sure is one of the driving factors.

"We cannot risk looking outdated". So weak management, probably.

But also talent availability I suppose. If there's a new trend, the pool of people you can hire include many that are in on that trend.

UI frameworks too, probably. The modern thing™ does the modern thing™ and you do want to be on the modern thing, because you fear that only that receives security fixes or whatever.

Make-work. Managers needing to justify their promotions with a new way of doing things. Whole teams are given a reason to stay employed. OS and device obsolescence is achieved. A win all around, save for the consumer.