why do sports fans feel so compelled to wear the paraphernalia of their favorite team(s)?

What do they get from it? For example: Jerry Jones is one of the most high-profile owners in the NFL. Buying Cowboy's merchandise like, Shirts, sweaters, hats, shoes, and etc. The money for these things goes right to his pockets and essentially, you the fans, are paying him to advertise for him. Why would anyone do that!?! If he wanted to get to know me and my family and spend time with us, I'd take an interest in his business and if he asked to wear some of his stuff, sure, I'll help out a friend. But paying him to do it? Think of it this way: Job Bob owns a Croquet team. He goes around to people in audience wanting to know if they'd like to wear some of the T-shirts he had printed for his team and you are in that crowd. You don't know him and he doesn't know you but hey, he's offering, so sure. But then you find out he wants you to pay for shirts? How willing would you be and how is that any different than a major sports team?