Speaking generally, you only have to look outside of your window to see the problems. Snow and ice are preventing a sizeable proportion of the population from getting into work. That is not just aircrew, but check-in staff, baggage loaders, cleaners, fuel truck drivers, ground handling staff, ramp supervisors, de-icing rig operators, air traffic controllers, bus drivers, security staff, etc.
Most people are working around the clock, extra shifts, days off and overtime to cover for absent staff and to cope with the unusually high workloads.
None of this is aided by Gatwick Airports abyssmal performance at running a major international airport over the Christmas period. That notwithstanding, all of the staff who work there, and the airlines are still trying to achieve on-time dispatch, or the closest they can possibly achieve given the disruptions they are currently having to contend with.
Obviously in many regards it is a constant juggling act. With that in mind, you need to ensure that as many of the variables as possible are regularised. Clearly passengers need to be at the airport on time (although many will still be late for all the same reasons,) so that you are in a basic position to dispatch if an improvement can be implemented.
It often happens that aircraft, crew and personnel are substituted where an otherwise delayed flight can be dispatched because all the other variables are ready. Sometimes that happens, sometimes it doesn't. The problem with delaying passengers is that it not only guarantees the anticipated delay, but it also invites further additional delay for a whole host of scheduling reasons. In other words delays are often easier to manage than simply re-scheduling a flight into a new departure slot where for example baggage loaders are not available until a gap appears in their programme.
In the current operating environment I would be grateful the delays are only running around 3-4 hours as it affects your flight. They have been in excess of 36 hours over the last few days, and disruption is likely to continue over the next few days.