They try to attract more people to play sc2. And make developing arcade games for sc2 worth the time, as more people would have access to the map.
I'd like more if they made melee more interesting. At the moment even in gold league you need to know builds, and work hard in game to succeed . That's geeky, not entertaining.
Arcade maps, such as tower defenses, squadron for example, are awesomely entertaining and not that geeky. I guess people will love free arcade, yet I think SC2 team should make melee a bit more attractive. Hope we see something like that in LotV.