Or "platform decay" if you need to talk to your grandma about it.

Not really the right use I think. It was coined specifically to describe platforms' lifecycle of changing who they benefit. What's above is just constant churn in the attempt of infinite growth or just hanging onto market share trying to decide what people want (or tell them what they should want).

Here is how platforms die: first, they are good to their users; then they abuse their users to make things better for their business customers; finally, they abuse those business customers to claw back all the value for themselves. Then, they die.

A paid subscription service like O365 or spotify isn't too similar to the advertising "business partners" of a social media platform like tiktok. Of course language is descriptive rather than prescriptive but I feel like overusing this term loses the perceptive observation (and the message Doctorow wants to promote) of how these businesses work. Microsoft adding new features and spotify changing things to either make their app management easier (they claimed that's why they got rid of android widget for a while) or promote their own stuff doesn't seem to fit.

Normal part of monopolization.