That's a pretty busy schedule - what happens if the poor old aircraft goes "tech"? - if fully loaded then any replacement 777 would be unable to accomodate the 336 passengers!
There's a 'cap', I believe, on the number of passengers for a while, as the number of refurbished planes increases, so to avoid too much mess in case of a tech aircraft change. However, it has to be said that Gatters uses their planes pretty heavily, so that schedule is nothing out of the ordinary for them.
This is only my understanding and might, or might not, be company policy.