Well there is more "dirt" on the ground than in the air.

They have them. I use them on some engines... You just need to weigh the effect of adding an additional failure point to the lower level of dirt typical in air. Actually, mostly what I've seen is flying insects that get sucked in and cause flame outs. I think that is probably more an issue than any dirt on a flying vehicle. I use to fly on farm land and the number of insects eating up all of the agriculture was enormous....