Echoing what DoudJr said, making two maps would split the player base creating huge queue times for one or both maps (especially if you want a balanced match based on skill tier).
Also, playtesting a new map would take quite some time, and would possibly change the required number of players on each team. 2 lanes could mean 3v3 is no longer possible. You could have 2 laners and 1 jungler, but matches would be longer (assuming turret health/damage output stayed the same). Balancing will...
Posted: Jan 26, 2015