I don't have access to the Next.js telemetry data, but I could definitely need to ask the Next.js team from time to time: "so, are your users more using Yarn workspaces? Or npm link? Or something else?", etc.
For the same reasons some people complains about Ubuntu removing some features because they say "people don't use it", while people using those features tend to disable the telemetry. Sometimes, telemetry is useful.
It is not to spy on users, it is about making the best technical choices to ensure the best Developer Experience.
_edit: typos_
Also, about removing features based on telemetry, of course people are going to disable or block data collection and you will make decisions based on incomplete data. If you must remove something, do it because it makes sense and it fits within your vision for the future of the project you maintain.
There are major OSS projects with no telemetry that are hamstrung by their lack of insight about which platforms and systems their software is running on.
Everyone should have the right to turn it off, but I think this is going to become the norm.
And this isn't just for their official hosting service? That would be much more understandable
I remember discovering this a few years ago and was so annoyed that it was on my default and had to have this in my .npmrc:
metrics-registry = null
send-metrics = false