I imagine that they probably have more pilots than usable aircraft at any one time. Combat aircraft are very complicated to keep in a ready state, so you're going to have aircraft that are unable to be used. Adding more aircraft or even just spare parts is going to enable them to increase their sorties.

Regular aircraft require a significant amount of maintenance just to fly safely, now add even more systems to that - radar, more communication gear, countermeasure/defensive systems, then the weapons, and it gets even worse. Then when you look at fighters, that can undergo extreme stresses, it compounds everything.