A couple of things come to mind on this:
1. Gatwick is presently operating North Terminal only and even though movements are a lot less, if a flight arrives a lot earlier than scheduled then there may not be a suitable parking contact stand available. The alternative would be to park remote which could result in no busses being available for a while or not at all.
2. Ground handling may also not be available immediately if arriving much earlier than scheduled with the handling teams not planning for the early arrival and occupied with other flights. .