I don't think we've ever had any statistics on how many people actually participate on these. I only played a bit during MoP where I ended up with 3 max level pets, then I couldn't be bothered anymore. If I wanted to play a Pokémon type of game I'd actually play Pokémon, this is just a cheap knock off. But I think the rewards are whats pulling people into doing them. At least the menagerie in your WoD garrison had some good stuff, not sure if they have more like these.