I don't have any problems finding a campsite. Yes, it means planning ahead, but it works.
There are many different systems out there. If the places you are trying to book don't work for you, you might try looking at other ones.
For example, if you find it impossible to stay at RV parks with full hookups, you might start looking at places with electrical only or dry camping.
Perhaps adjust your stay dates. Look for shoulder season dates, etc.
There is no one reservation system that works for everyone. For every person who finds a system lacking, another finds it completely doable. The trick is to find a system that works for you and stay at places with that type of system.