How did League of Legends become so popular?

The popular predecessor of League of Legends, DotA, was one of the very first and most popular in its genre. However, people believed that the game needed to stand-alone from the Warcraft engine and be more available for online play instead of LAN. When the DotA community heard of Riot Games’ idea to build an online MOBA game with a stand-alone engine, they were very supportive and eventually made up the very first player base of the game.