I feel your pain. It can be impossible to get into some parks. Why? Because they're awesome and everyone wants to go there, it's that simple. Even if someone changes their reservation, another person takes it immediately. You won't see a popular campground like that with empty sites, they're too popular. People complain about "cheating" etc to get a reservation. The problem is supply and demand. Too many people want too few sites. If people stop altering their reservations and only book for the exact days they want, not much will change. There will still be a ton of people complaining they didn't get a site.
I managed to get a site at Assateague island in Maryland this summer, (I think practicing with Michigan state parks gave me skills to get the site..... ok it was probably just luck!) I like how they do their reservations. They open booking for an entire month at a time. All sites for the whole month were gone in a minute, but it prevents anyone really from over booking. You take what you can get. Good and bad with that just like Michigan park system. No system is perfect.
