I mean, obviously it’s a confluence of many compounding factors, Stranger Things and Critical Role among them. The Covid pandemic was also a huge boost, though the snowball had already been going for a good, long while by that point.
I think, if I had to identify a common element among all the things that have been contributing to D&D’s incredible increase in popularity in this particular moment though? It’s the proliferation of fast, stable internet access. That’s what enabled Netflix to become a thing, it’s what allowed VTTs to get better, it’s what made live-streamed Actual Plays possible, it’s what made the books accessible to people without having to go to specialized hobby shops, allowed people to easily share homebrew… And it has been a major contributor to the increasing social atomization and isolation driving people to seek out more social leisure activities like tabletop gaming, which the pandemic then accelerated to an even greater degree.