Most rides have a set limit amount of participates it can support, and if it is a particularly popular event then they want to make sure they maximize the amount the event will receive by setting that as a barrier to entry. Not so much about making sure they cover the cost of support they do that with the event fee. They want to raise money and as such reach out to all the participates to crowd-source the fund raising. You can not have an infinite number of participants and some events get set to rather low numbers under 2000 due to local constraints set by outside forces (local police, regulations, venue size, etc).