Most of them aren’t.
User data are more than post/comment history and likes. Where do you connect from (no matter whether it gives hint about your relationship status or your work and customer), which comments you didn’t write, which device you use to connect and more.
Lemmy instance I know, don’t collect much data, hence the short term of services and the lack of cookies pop up unlike big (social) media sharing their data with hundreds of " partners"