I share your pain because I've had some difficulty booking May in California even though I started early. Forget Yosemite even trying the second res opened. A music festival ruled out the convenient Napa Fairgrounds, something else ruled out the Monterey Fairgrounds, and my res in an Army COE site in Ukiah was later cancelled by the facility due to damage from the terrible floods. Now storms have damaged and closed a bridge on the Big Sur highway. Commercial campgrounds near the coast are pricey and want 3-night minimums for Memorial Day. So I've had to roll with it and search for different options and routes.
I don't think there's any privileged group, though, that always gets all the weekend, prime, waterfront sites they want. Same scenario for any state park in the Florida Keys, and people post here now and then about how there's a mythical deep/dark-web system others must be using to get sites.
The truth is sometimes you will succeed with the 3-computer system the very second bookings open. Or then you book a nice commercial campground or do what others suggest, and keep looking for public CG cancellations or get happy with some inland places that may surprise you.
The first time we went to the Keys in our RV, it was because a kind poster on this forum alerted everyone the time and day he would be cancelling a week in a state park there, and we booked it that morning.
Some of us like to make most of our plans early but many prefer to just show up hoping something is open (we don't use that last method for the Keys, but know others who did and got exactly what they were hoping for.) But if you do, have a Plan B in mind.
There's no doubt that weekends and holidays may cause you problems. Another truth is that some older state parks have mostly smallish sites, so if you have a big RV, your chances of getting a site decrease.