Reddit seems to have reversed course with making users sign in as well (or my adblock has updated and removed the forced login modal or something.) but my thought was simply: "Well, I guess I just won't view Reddit content anymore, big whoop."
I don't know if Reddit are doing it less now or not, but it's worth noting that it's always been somewhat hit and miss.
I suspect a mix of very data-driven testing (to try to show it to people who will login, and not show it to those who'll just bounce), and technical debt confusing things. But often it will vary not only from one person to another, but even for the same person between two different web browsers, or connected through two different IPs, or whatever.
(I'm not necessarily agreeing with this; after all it's trivial to make an account for an AI company. I'm just saying that's the reasoning behind it)