I'm guessing mid-air refueling has constraints on windspeed and wind direction, visibility, and precipitation. I may have missed some, but those alone make me feel like mid-air refueling can't be done most of the time (?)
About wind direction though, I guess you could just fly in the "right direction", but then this would also have constraints because the "right" direction could lead away from your ultimate destination.
(also, is there a mid-air refueling tag I couldn't find?)