Why was chess considered to be one of the most difficult games for computers to play well?

In a general sense, the answer to that is Go. The main reason for that is because the size of the board and the fact that it is empty to begin with gives the game a much more complex opening to the game. But if you were to make things equal in board size then chess is the obvious more difficult game to master.

Explanation:

Chess is considered a hard game on computer because it is very hard to learn and play.

Explanation:None.