Dota was first, and has a much edgier theme. So yea, of course MLG is gonna prefer it. Not to mention that its considerably harder than league. Target cc that lasts over 5 seconds, damage dealing abilities with global range ( that arent skillshots ), 1 hitting full HP champions from stealth that lasts 35 seconds, and tons of other things that require very in depth planning to avoid, that league simply cannot compare to.
Dont get me wrong. League is funner, league is a great deal easier to understand for new people, and its funner for everyone to play. But DOTA is harder... A lot harder.