I think there are too many airlines with HQ in some countries, like USA and China. Maybe there are 20 or 25 different airlines in a single country and you can't find any profit. Adding a limit of, maybe, 10 airlines per country we would solve that problem. Or you could put a different limit of airlines in every country.
For example: USA, high rate of passengers, limit of 15 airlines
Spain, medium rate of passengers, limit of 8 airlines
Iceland, low rate of passengers, limit of 3 airlines