Hi CTSVdriver,
You might as well ask the USGA that question. The US OPEN, in real life, is Open to anybody...who Qualifies!
From your avatar I assume you play irl. If your handicap is low enough, You could enter the qualifier rounds and maybe play in the Open. Anybody can, hence the "OPEN".
Would you work on your game to get your handicap low enough, qualify, and win the open? I know My game isn`t there :D, But I do have the opportunity to try, again...hence the "OPEN".
Meanwhile, I`m glad that we have an 'OPEN" here, even though I can`t win it (or can I ;p, next year!).
I joined WGT last year during the qualifiers for the Open and didn`t stand a chance to qualify. I still tried and enjoyed the experience. I worked on my game all year and qualified this time, but didn`t come close to winning. Who knows what`ll happen next year?
One thing I will say in answer to your question is, another question. What would be the reaction if "The Open" was Exclusive? Kinda ruins the title of the tournament ;).
I`ll just keep practicing and watching "Tin Cup" for inspiration :^). Cheers