Dota2 is for those who want a harder and more complex game, lol is for those who want a simpler game that's easy to learn.
Dota2 is closest to the original Warcraft mod which had a steep learning curve and stays closer to the feel of the original heros. Lol just too the same concept of heros mixed with tower defense and made it look all fancy with highly stylized heros and big breasted women, while simpilizing the gameplay enough, and improving on separating skill levels and made it more open for casual players and elite players to both play, and not ruin each others games