Why? Because the AMA IS a community based organization. And, it just happens to be the ONLY community based organization that has spent over $1M working with the FAA and Congress on behalf of model aviation. What they have accomplished is amazing.
Now, if your local club would like to spend time and money to work with the FAA to become a recognized community based organization I don't think anyone is going to stop them. I, for one, would be interested to know what your local club has done to date, working with the FAA and Congress to help protect the model aviation community from over regulation. What AMA has done is huge and well documented.
And, BTW, the AMA is NOT an insurance company, they buy insurance from an insurance company on behalf of the members to get us the lowest rates possible. I suggest you do a little more research.