Fray, in addition to what Speeddial said, in civil aviation you sit comfortably in an armchair at 4000 feet of so straight and level with some possible exertion every few hours of so.
In a combat jet yoy may be sitting on a less comfortable seat, at 25000 feet, pulling high gee. Then you might suddenly be sitting outside your comfort zone at 40000 feet and plummeting for the sandpit and bad guys with big sticks.
How would you propose to use your inhaler under these circumstances?
As has been stated elsewhere on the OASC thread, there are more than enough super-fit, high quality candidates for the few slots that there is no need to take high risk, marginal candidates.