I travel out of Gatwick about 2-3 times a year, a use the road parallel to the runway (Charlwood Road) on a regular basis and nearly every time i pass the runway I spot a virgin Atlantic 747's parked in the cargo area, mainly LHR based 744's but sometimes LGW based 744's and i can think of any reason that Virgin would keep aircraft there as they have such tight schedules at Gatwick, could there be a possability for some new routes or additional services?
Sure, schedules could be changed to achieve a higher aircraft utilization rate. But people cargo (err, passengers) like departing at normal times and flights that depart at the same time daily. Regularity is the spice of live.
Machines break and quality needs to be assured. No one wants to be in an airplane when it breaks. Virgin needs time to maintain and inspect its aircraft. New and replacement seats take time to be installed (one to two months), new avionics, etc.
There are loads of other reasons (crew work rules, noise rules, etc) but the two above would cover 65%. Virgin could add routes but would they be profitable? Would people book them? More than likely no. Would the additional flight compromise Virgin's marketing (new seats), safely (maintenance) or new avionics? Maybe VS should add a FCO tag on in the summer, MUC for OFest, and the four times a week TLV (friend would love that). Besides that, VS can't do it.