Two major reasons: The first being that Dota is a team game which requires teamwork to win. This presents a new challenge of having actors work towards both pe

Two major reasons: The first being that Dota is a team game which requires teamwork to win. This presents a new challenge of having actors work towards both personal and team goals in a balance (much like real players) to be able to win, which is very difficult to train. The next is that Dota and Go are two very different kinds of games. Go is an "information complete" game, where all players have access to the entire game state at any given time. Dota, on the other hand, is an "information incomplete" game, as teams are vision restricted: there's no guarantee on the state of anything out of vision, meaning that the AI has to develop what most players call "game sense" in order to be effective. On a tangental note, it's also an interesting problem from a state space perspective. Go is technically "solvable" to a point where you could (with a currently unobtainable amount of computing power) find an optimal move, but Dota is almost unfathomably more complex: 10 heroes picked from 115, each with the ability to hold any combination of 9 items from about 150, with abitrary health and mana values, at abitrary positions on a large map, not even mentioning the non player units (creeps and neutrals). If Go's state space is our solar system, already a difficult scale to comprehend, Dota's is the whole galaxy. [Typed on mobile, apologies for any typos.]