LAX-MCO is one of those unpredictable routes. There is a large film industry in MCO, and as such that route is susceptible to being full of paid F pax. Plus (although this applies to LAX-MSY as well) there is a low F to Y (1:11) ratio on the 738.

I have never taken the route, but I have a friend who is PM and makes the trip 3 or 4 times a year. He says you can find yourself clearing at the window for the Monday morning flight one trip, and then the next time be 10 deep on the u/g list for 0 seats on a Wednesday red-eye.