British Army With No Tanks!!!!!!!!!!!!!!

[Legbreaker]

Fixed wing aircraft simply have less moving parts than rotary. It's just logic that they require less maintenance time and effort.
Ground vehicles have the added advantage of not needing to fight gravity. If something fails, you don't have multimillion dollar machines falling rapidly earthward to smash into a million very expensive bits. A ground vehicle can often still be function and add at least something to the battle, while putting a less than perfectly maintained aircraft into the fray is quite likely to result in the complete loss of the machine and crew - if it's even able to get off the ground and into the battle in the first place.

That said, adding a third dimension to the battle is ALWAYS a good thing, but it comes at a cost.