I suppose if you're measuring difficulty of a game as how difficult it is for a human player to beat the current masters, then that seems a little unfair. Poker has been around for less than 200 years and the current variants are less than 100 years old. Chess has been around since the late 1400s according to the Wikipedia article. There has been a lot more research and time spent on chess, and the community is consequently much more mature and skilled.