AFAICT in ~Dec 2024 the reasoning was that they had a paywall.

I don't know what percentage of their articles were behind a paywall back then, or the relative change to now. (Well, except for the fact that clearly some of their stuff is public today since we're looking at it.)

If I had my 'druthers, "paywall" and "register-wall" would be little icons on individual submissions. Then people would choose whether to upvote a more-accessible option instead, whether the hard-to-read stuff was still important enough to commenting on, etc.