I mean, your first sentence almost contradicts your own point. You said you remember this happening with two mega hits, then said that it only really happens with mega hits anymore.
I think your overall point has merit, but I think it's less about the algorithm, because you'd almost think that logically, because of algs driving people towards content similar to their peers/friends, it'd drive more shared discussion offline. At the very least, I'm sure that's what most of these media orgs hope for, too.
But the issue is that there's just so much MORE content out there now, it self-cannibalizes, outside as you said, mega hits.
The discourse over network television sitcoms I'm sure is long dead. I bet back in the 70s-90s you could get watercooler chatting about the latest weeks episode of the hits. Friends, Seinfeld, etc etc all probably had people talking about latest episodes. But network television is basically dead and to your point, everyone has much more personalized media feeds, thanks also in large part to just having so many more options, people can be more picky.
I personally also think that capitalism has been driving the overall quality of most content down on average, as organizations continue to cut corners, pay workers less, rely on mass automation and steer away from the traditional arts towards computer generated content (CGI over hand drawn, or miniature sets, real life sets, etc etc ad nauseum). So we're also just getting less 'viral worthy' content on top of all this. But that's just again personal disillusion with media as a whole, especially as I get older, and we continue to see massive corporate consolidation.
End note, which others have already touched on. Communities are definitely still having these live meta discourses of current events, media and non, but it's almost all online now. Snapchats/IG between friends. Discord servers which are all private and unquantifiable. Tiktoks which I see this A LOT, tons of people posting viral reactions to live events, it's like a huge part of that culture. We're also increasingly not spending time with eachother anymore, period. It's a known quantity. We just all hang out less, spend less time in social places.