There's gameplay; they're just not interested in offering that sort of gameplay to people.Blizzard deliberately never did player housing because they viewed it as pointless since it has no gameplay associated with it.
Creating things in a video game environment is gameplay. Building games are still games. Remember Spore? They released the character creation part of their game as a teaser, and it did better than the game itself because making little critters was the most fun the game had to offer.
Blizzard just isn't interested in offering creative gameplay. They want to keep the creative fun for themselves, and use it to produce art and content for their users to consume. They make all the creative decisions, and give you tactical and resource management decisions as gameplay. It's a valid approach to making games and developing memorable (if derivative) franchises, but it does limit their user base to people who don't care for any sort of creative gameplay.