The problem with DCS for civil aviation is the tiny theatre, poor ATC implementation and lack of navigation aids.
FSX, P3D and X-Plane have pretty much an entire world to fly in with accurate runways, frequencies, terrain, weather etc.
Those guys don't want to fly their tube liners in circles around Georgia while trying to avoid being shot down. They want to file an IFR flight plan across europe or the Atlantic and use Vatsim to talk to real controllers on the ground.
It's a completely different kind of simulation and something that DCS just isn't able to offer right now.