There's plenty of scripts out there that are designed to play poker. The problem is that you can only program it as far as probability and strategy. No one has really developed an efficient enough algorithm for predicting players moves or hands.
Chess is a game of raw computing. You run through all the possible moves determining which one will grant the best outcome. It's an unfair comparison because in poker, the computer can't predict from the standpoint of its opponent. There's also so many more variables in poker. (stack size, raise size, position, raise frequency, fold frequency, players still in hand, call frequency, raise sizing, board card probability, etc... )
Someone will eventually develop software that runs through data from millions of poker hands played by real people and finds the most similar position of the hand being played to make a decision. (If they haven't already) The problem there is that no hand is the same. That's where the algorithm part comes back into play. It's going to happen though.