well, most people get bored in long games, so short&easy-to-understand(what you called "crappy") games are getting popular fast, because of those reasons:
1. they don't require thought so every noob on bnet jumps into them, what means that you can fill up all 6/8 slots in 10 seconds and play right away.
2. the map is short and you actually have a chance to finish it.
3. it has no storyline, complex mission, or time when you need to think what to do, you just follow the most non-noob in the map till you get good at it yourself.
4. most times you an just do nothing and chat with the other players. chatting is fun!
5. if you're the creator of the map, it takes you only 5 minutes to make the map but you recive weeks of glory from tons of players that get to play it.
6. you don't care if someone steals that map, since you didn't put any effort into it anyway.
moral: maps like "Don't F**kin' Move" and "Last Man Standing" are fuuuuun
