Apparently we use different online systems. For most all TX State Parks for example, you get quite a bit of information from their online booking site. Site length, site pad composition, full/partial/no shade, amenities, distance to bathrooms, etc. etc. and for most several images of the actual site. Similar particulars available for other State Parks as well.
As for your comment "...you do all the work online to book a campground" I don't understand what you're saying? Yes, one has to consider the options and make a decision. But while it may be frustrating at times when you want to make some kind of adjustment involving the fees, it's out of the hands of the park staff and you have to deal with the reservation system. Frustrating perhaps, but in most cases the staff on site has enough to keep them more than busy without having to deal with payment issues.
Actually, the times that I've had to call "central booking" to make some kind of change concerning fees, I've had nothing but great, helpful service. Of course they all want you to try to do it yourself online, but when you end up calling to speak to a real person, they've always been most helpful. This goes for various State Parks we've had to call as well as ReserveAmerica.
Private Parks? I know nothing. Never use 'em...