I believe the fact that you don't have to stand in line for an attraction leads to greater wait times. All you have to do is scan your wrist band and you're in line. Therefore, everyone in the park should be in line for something at all times. There's no excuse not to. This leads to drastically longer wait times, which is something the guests are obviously not responding well to.
Normally, when guests are eating lunch, they're not in line. When they're shopping they're not in line. When they're taking a break they're not in line. Nearly every single person you see in Volcano Bay should be in line for something. When 95% of the park is basically in a queue, that leads to longer waits, or much lower capacity, or both.