> continuous UI updates are frustrating for users […] It's driven often by individual developers' needs to leave their fingerprints on something, to be able to say, "this project is now MY project", to be able to use it as a portfolio item that helps them get a bigger paycheck in the future.

Yes, although users also judge updates by what is apparent. Imagine if OS UIs didn’t change and you had to pay for new versions. So I’m sure UI updates are also partly motivated by a desire to signal improvements.