Thing is, especially in sandy environments, Helicopters have a few weak spots. The rotors cause massive torque on the drive shaft, and fighting against strong winds increases that. Also, and more importantly, the Engines take a hell of a lot of Air, and the turbines generate the power that keep the gyro and other stuff balanced up and keeps the chopper level.
If sand manages to clog up the brushes in the generator or work it's way into the driveshaft, you end up with a situation that may cause a crash.
However, that said, someone needs to go kick some of the ground crew up their arses, they should be checking those things before every single flight.