I think it used to be, but IIRC some time after Stack Overflow became popular they started actually gating it. Probably because there were people researching questions posed on SO and answering them from info on EE.

If so, that was a catch-22 for them. Either leave them available and watch the only thing making your site useful be rapidly transcribed onto a different and now more popular site (whether by people playing into the gamification or scraping as used to be the norm doesn't make a difference here), or close it off and allow their more use hostile experience to force them into irrelevance. That's a tough place to be. By the time it became an obvious problem SO was probably too far ahead to catch even if they pivoted immediately, as I'm not sure anyone ever really felt any loyalty to EE with it's poor usability bordering on UX hostility.