Yeah, I've noticed that too. From what I understand its difficult to
hold events on public land because uncle sam wants you to buy really
expensive permits to do ANYTHING organized like an event. That's why
private land is the best route and the only private land so far for
sandboarding is Sand Master Park. You can ride just about anywhere
they allow people on the dunes, but actual events are what cost.

But that's just my opinion. I could be wrong.

Later...