Most great games never get anywhere near this much buzz.

I think it's a product of the genre. BG3 is in the CRPG category, which had a bit of a resurgence lately between Pillars 1+2, Pathfinder 1+2, and (perhaps most relevantly) DOS 1+2. Good games in an existing category of game helps build up buzz in that category and more players. More players creates more demand... but there hasn't been that much being made in the CRPG bucket lately.

Then, on comes BG3. It fits in that bucket. It has much higher production values than the other recent games in that bucket. It's got one of the most valuable CRPG IPs attached to it with Baldur's Gate. And it's reportedly amazing as a game on top. The last part wouldn't get it anywhere near this much attention on its own, but in conjunction with the others it's gotten lots of buzz.

I also feel like Larian handled the early access part really well for keeping the game in discussion without making the game oversaturated in gaming circles. They got a lot of "free" (not actually free, but you know what I mean) marketing out of that.

It's that simple.