The idea is to balance the need to preserve history (community interest) and the need to protect users (individual interest). We don't get there perfectly, but I can tell you for sure that the vast majority of people who ask us about this end up happy with how we help them.
Might be the copyright reform, but comments should still be fine with that.
FWIW, I completely agree with you on the chilling effect of upload filters. But upload filters aren't part of GDPR by any stretch of the imagination.
It also might not.
It might be worth it to some company to determine which it is, but who would expect that company to be Microsoft?
MSDN comments still exist and Microsoft operates several forums. Perhaps GDPR is a questionable excuse for some lazy sysadmin not wanting to migrate comments, but it doesn't fly here.