There are many other applications for data than just ad targeting.
The pushback here may seem paranoid for the specifics of this particular case, but that's because it comes from a more generic and IMHO perfectly justified position of treating all telemetry as risky by default, and all attempts at making it opt-out as wrong, dangerous, and likely malicious.
The arguments "for" are all based on assertions about this particular case at this particular point in time. The data to be collected is benign. Collecting it will translate to meaningful improvements being delivered faster. The people behind the project are all nice and reputable. And so on. In contrast, the arguments "against" cover the possible future evolution of the telemetry itself, as well as the project and the people behind it. The set of metrics and reporting frequency can change. The goals behind it can change. The nice people might turn naughty, or be replaced by scoundrels.
The arguments "against" include, in particular, building the precedent and infrastructure. From that point of view, you saying:
> set of static, anonymous metrics, updated _once_ a year from a tiny fraction of developers is not worth the effort to even ingest into some targeting system
sounds to me like me saying "this browser extension, which code I audited myself, is only reading the account numbers and names from my banking page - it's really not worth anyone's effort to do anything naughty with it, so there's no reason I should be afraid of giving it full read and write permissions for the banking page, and no reason I shouldn't leave the 'auto-update' checkbox on".