They were probably understaffed. Trips like that tend to rely on parents volunteering as chaperones, and they almost always just barely meet the requirement because schools are already understaffed. That said, they are required to have medical kits both at water parks and with at least one chaperone on field trips- they could have at least taped OP's toe to another toe so they could walk around, considering that's all a doctor would tell them to do.

I teach high school and through my experience planning field trips, if the school didn't have enough chaperones, the field trip would not have been approved by the school or the water park and would not have happened. Parks like that will often check that the school has provided the right amount of chaperones before letting them in. Also, I know I would face repercussions from my school if I didn't make sure the injured kid got medical attention—even if I had to leave to go to the hospital with the kid. That being said, when you do large group trips with high school age kids to a water or amusement park, the kids are not with a chaperone the whole time, so it's probable a chaperone or teacher didn't even know about the incident or how serious the injury was. Most of the time chaperones on those trips have no idea what the kids are up to (which kind of negates the whole purpose of chaperones…).

Broken toes often require little medical attention. All they can do in most cases is tape it to another toe and wish you good luck.

I think sunburn would be the least of my worries if I had to stay that long in the sun.