It's interesting that you can play any 5e adventure without ever having purchased a single core rulebook. If an adventure gets a good reputation, it's a good way to pick off sales from people playing a competing game, without ever committing them to 5e itself.
In fact, if they publish a fun adventure where you can start and finish the whole thing in one session for like $5, I can see people buying that even if they primarily play another game entirely, just for the fun of it as a one-off.
Seems very smart. There's zero barrier to entry for the game now. You can pick it up...anywhere, with any book they put out.