I suspect it is not that they totally block C2C it is that belonging to the network only means you have to provide a certain number of sites per day. I don't think it is just weekends. I know that my home park only sets aside like 10 sites for each of the reciprocal programs it belongs to and will not vary from that. When they are taken no more are given out.
On the flip side we often go to a park on the Oregon coast under reciprocal programs and home park members who are guaranteed a site are sitting in overflow while we get a full hookup.