Poker is actually harder than chess in many ways, even though it doesn't always feel that way. In chess, both players can see everything—there's no hidden information. If you're better, you'll probably win. But in poker, you don’t see your opponents’ cards, so you have to make decisions with incomplete information—and that makes the game much more complex.
Also, while a computer could 'solve' chess decades ago, poker took way longer to crack—even just a simplified two-player version—because there are so many more possible situations, especially with
bluffing, different bet sizes, and psychology involved.