I chose poker because I love the competitive nature of the game. It is so complicated and the amount of math and endless types of situations that occur draws me easily into the game.
Simply put; it's challenging and fun. Not only is it exciting to feel the adrenaline pumping and to win a tournament after some bad beats, but you can actually gain money. It's not gambling if you play with the right bankroll, study and play correctly over a large enough sample.
Progress is also easy to follow, and when you see that all your studying and practicing has paid off, there aren't many other things that can exceed the level of satisfaction you're experiencing.