The bottom line is it's expensive. The weekend at The Rock with travel, hotel, food and shooting would have run close to a grand and as I'm leaving for Wyoming Thursday it just wasn't in the cards. Next year I plan on going. I think three days is plenty of time to burn powder and reconnect with the guys you saw at the last shoot.
Timing always plays a part in the attendance. as mentioned previously the Fall Southern is well it's in the fall during the peak of Grouse season here and birds win out over targets, The Rock is on the cusp of bird season but it's still early enough that it doesn't really interfere.
I agree with Craig that most of us attend these events for the fun of attending and not as serious competitors. If there was a way to shoot and enjoy the camaraderie but not for score at a lesser cost more targets might get thrown. A Lewis class system would even things out some as well.
A person can only do so many shoots/trips in a given year unfortunately.