Well, speaking just as a pax who has used this route, there are more flights to MCO than any other VS route from LGW (at least 2 a day, year round I think), so I guess statistically there is more chance of a delay.
MCO can also be quite weather affected, and probably gets more thunderstorm days per year than some of the other VS leisure destinations.
Also VS use MCO to swop the LGW and MAN based aircraft around, bringing the MAN-based aircraft to LGW for maintenance within the schedules I believe.