Alligators need oxygen too
They can stay submerged for up to 20-30 minutes (some say up to 24 hours), but must lower their heartbeat considerably and use anaerobic respiration to stay alive. In this state, they are in no condition to fight prey, as they need aerobic respiration for intense muscle activity.
Gators’ advantage is, once they have a mammal pinned underwater, they can outlast the mammal
This man had his own O2 supply, so he could outlast the alligator. And the gator could only keep a locked jaw grip, and was unable to respond, or fight with him underwater
Makes perfect sense........................