I am a big fan of the Rays. Yes, tickets are cheap ($13 for outfield seats), but I have RL to deal with. Besides, who wants to go to the park and pay $7-9 for a stinkin beer and $4 for a dog after having to pay $20 to park. For two people, it can get pretty danged expensive. The only times that I have gone this year, was when someone gave me tickets. Don't jump on the Rays fans like that. There are many other teams out there that cannot fill a park either.
You also have to understand the sports climate in this area. The Yankees have there spring training headquarters in Tampa. Have for a very long time. They are a large draw to the park when in town. The Red Sox have their spring training in Fort Myers which is only about an hour and a half away and are another large draw when in town. Tigers here in Lakeland. The Rays have only been here for ten years. They needed something like this season to draw the fans in. You will start seeing more fans in the seats next year.