I know Monster of the Week has had it's finer points debated and found lacking but, it seems to be a lot of people's (mine included now that i think about it) first pbta game coming out of 5e

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I know Monster of the Week has had it's finer points debated and found lacking but, it seems to be a lot of people's (mine included now that i think about it) first pbta game coming out of 5e
I think that it helps that it's distinct enough from D&D that it doesn't fall into the "why don't we just play D&D?" trap that I imagine Dungeon World has.
"Monster of the Week" is also just a very evocative archetype. Most people have seen a Scooby Doo, or Supernatural, or Buffy, or read Goosebumps, and so on.
Honestly think Supernatural is probably a decent chunk for it's popularity, plus, as graham said, the McElroys.
I think its mostly because as far as PBTA games go, its relatively simple without many subsystems, and has an easy-to-grasp genre touchstone. I mean, hell, I can still teach people how to play in 10 minutes! (There's a reason Bones and Story is starting out with it, even if we do wanna go to more feature-rich games in the future)
Of course, comparing it to today's games, it definitely is lacking modern PbtA design sensibilities. But hey, its walking proof that not every RPG is as hard to pick up as DnD is.