US Online Gaming

Recently I've wanted to get back into online gaming. I haven't placed a bet online in years, and I've come to learn that all my favorite sites have banned US players. I've heard that there are some smaller sites out there still accepting new, US players. But my question is, why do they have to ban online poker? Can't they come up with a taxation agreement with the major sites? It seems like a really good opportunity to make a lot of people happy. I don't know all the reasons why US Government made the ban, but they still allow brick-and-mortar casinos... Is anyone else confused?