Except that telemetry can give you more complete (and foolproof) information than what users report. But yeah, that could also be solved by having debug info that users can attach to their report, the app doesn't have to "call home" for that...

I agree, but it's a cost/benefit thing. Most OSS projects aren't big enough to do anything with the telemetry, so you're just paying in goodwill for no reason.