Its a bit of both.

Absolutely, for sure, a decent amount of telemetry is for simply making decisions about what people actually use.

“Should we improve (thing), or drop it and stop supporting it?”

Well, lets just track how many people actually use it first for a bit and then decide.

Youd be surprised how often users beg for features and then stop using them after 1 week lol.

But sometimes a random feature you thought no one uses much turns out to be actually quite popular.

This same goes for optimizing. Your highest traffic parts of your website are there you wanna focus the most on stuff being optimized to save money and improve user experience.

Do a tonne of companies track stuff just to sell it as data for training AI?

Yeah, they do. And its gross.

But there is a huge amount of telemetry thats just developers wanting to genuinely improve the user experience, catch bugs, etc.