Airforce etc are based on average damage from all people except you. You need to do more damage with air than the average person did total damage. If everyone does a lot of damage it's hard to be above the average.
For example:
A did 200 non-air damage and 1000 air damage (total 1200).
B did 200 non-air damage and 1100 air damage (total 1300).
C did 1200 air damage.
A lot of air combat happened between everyone but nobody gets any award because the best air dude was C, yet his air damage (1200) is less than average total damage from the other people (1200 + 1300) / 2 > 1200.
Meanwhile in a 90 second game:
A bombs two mexes, does 150 air damage.
B and C did nothing and rushed resign.
150 > 0/2 so A gets air award.
Some awards have a multiplier because their weapon type is rare (for example kamikazes are treated as x3) but air doesn't have this.