We travel with our dogs (under 20 pounds). Looked at a campground website we were considering and they do not allow the open top pens but allow the full enclosure crates. First thought for not allowi...
I daresay the primary reason has to do with people who leave their dogs unsupervised in the pens. We keep our dogs with us at all times. Others may not be as responsible.
We have our dogs on leash at all times except inside the mh. We've never had a problem but then we always monitor our dogs when out and about.