First, free users still have the right to complain. Freedom of speech. I have grievances about Windows and MS, and I don’t even use it.
Second, complaining is just words. It’s not like users of Gitlab are demanding financial compensations. They are just talking. It’s Gitlab’s right to choose to listen or not listen.
“You didn’t pay for it so shut up you entitled free user” is one of those ideas that just don’t work in practice.