Why does it say that on the coverage map I should get service when I don't?

I was in Fish Creek- Peninsula State Park this summer with other family members who had Verizon and they had no trouble with service, but I didn't get anything unless I was connected to wifi. I understand that I was camping, but this is a popular vacation spot and the map for coverage says I should have been fine. Usually this wouldn't bother me because I try to disconnect when I am camping but I needed to be in contact with my petsitter and coordinating plans with the rest of my family at another site (both sites, no service for AT&T) was a disaster! I just think it's a little embarrassing and it makes me want to get better coverage from Verizon. So I will keep them in consideration once I pay off my phones.