In Michigan the reservation system and number of sites and which sites can be reserved has changed over the years.
The change I noticed the most was the "Park Pass" requirement. Started out as a fee for day use areas as a paper tag on the windshield, like a parking pass. Then was included in the campground fee, eventually becoming it's own fee for use in all Mich. State parks, to be purchased as a day pass or an annual pass. Annual pass cost was about the same as 3 or 4 day passes. Now we have the option of having it added to our
license plate at a significant discount. Residents get a good deal, the tourists pay more of their out of state money into the system.
We used to call the parks to make a reservation, a couple of really popular parks had a lottery. But there were still non-reserved spots if you wanted to take your chances. Show up on a Tuesday fairly early and there was a decent chance you would get a spot. Often the most popular sites where NOT available for reservation. There were a few times when we showed up with a reservation for a site, and on arrival switched the site to one of those non-reservation sites since it was available.
Some municipal parks have implemented the same pass based system, Metro Parks in SE Michigan have day and annual passes good at all the day use parks.
Here is what annoys me. We switch to "user fees" that started out as a supplement to the tax support to provide extra revenue to improve the parks but has gradually replaced the tax support. And the parks don't really seem to improve much. Michigan gets a lot of tourist income and having good parks really helps. Seems to me we are mostly milking the past investments in park infrastructure.
Combined with the outsourcing of the reservation system which was supposed to "save" money but since the cost continues to rise I'm not convinced it actually costs less. I do miss being able to call the park ask a human that actually knew the park about sites, pest concerns, and availability. Now the campers do all that for themselves and pay more for the privilege.