That because the AMA wanted it that way but they should lobby for the hobby as a whole not just AMA members and not try to create a condition where all modelers have to join the AMA.
So you want the benefits of a lobby without having to pay for it? If you don't support the AMA you don't deserve anything from them.
You could start your own lobby without any financial help and fight for all your "friends" that wont give you a dime. Then I'll quit the AMA and enjoy the benefits you gained for free.