I think the key difference here is that ChatGPT and its ilk give an unlimited stream of yes-you-are-the-always-correct-genius sycophancy literally designed for

I think the key difference here is that ChatGPT and its ilk give an unlimited stream of yes-you-are-the-always-correct-genius sycophancy literally designed for engagement. The kind of niche rabbitholes existing from before LLMs are generally either rate-limited by being a limited number of actual people with strongly similar views (doomsday preppers, niche cults, etc), or so huge and chaotic that pure-strain sycophancy won't happen (reddit, 4chan).