The big issue with private CGs is the cost of land, especially if they are located in popular tourist areas. Since land is at a premium, they cram the sites in as densely as possible. They tend to be amongst other developed property, and thus usually contain a high percentage of permanent seasonal sites.
State parks (at least out east) tend to be in rural areas away from tourist attractions. There is significantly more land, as they are not near development, so the sites are spread out. However, even though these sites may be farther apart and larger, that does not mean the site is necessarily usable, especially for larger TTs. I've been to many state parks with huge sites, but the access to the sites is terrible. The entrance to the site can be on a severe slope, or the site can be littered with large rocks or trees, making it difficult to get the TT on the site, and then use your awning or slideouts.
The other down side of some state parks is that large groups of people can occupy one site. This can lead to a lot of noise and rowdiness from non-camper types that ruins the camping experience. It can be real trouble when a bunch of people decide to go camping and party all weekend long. They typically know nothing about camping ettiquite, nor do they care.
That doesn't necessarily mean you can't have that situation at a private CG....