They prominently use SSO, encourage the use of their app, and embed dozens of trackers.
They're actively trying to develop social features and get people to embed their identities.
This creates stickiness, a moat, and aids monetization.
Look to Twitter. They're forcing phone number association and blocking valid accounts from logging in without one. This will happen to Reddit too eventually.
On the other hand most people wouldn't want a completely free internet. 4chan versus Reddit and the public chose Reddit.