Sort of like calling the American baseball championship the "WORLD" Series when we're the only ones who play. Maybe the original intent was to encourage and create a truly international group of giant scale modelers; everyone else saw quickly enough that they could fly big planes without having to pay for the extra membership and not really get anything for it.

If anyone was allowed at an IMAA event without being a member of IMAA, what's the point of paying for the membership? Most people , IMO, don't care about the competitive aspects, they just want an opportunity to fly big planes with other guys who fly big planes, without having to deal with little planes. If you want to compete, there are the events like Mint Julep where you can build and fly for judging, and maybe earn a ticket to Scale Masters or Top Gun down the road, if that is your goal.
Don't get me wrong about IMAA membership, like I said before, the only reason I ever joined was to be able to go to some giant scale fly-ins and be able to fly. It is like paying for admission twice, because AMA is also required at these events. IMAA has outlived its usefulness, I think.