Cirrus, I would hazard a guess that it is down to money. There is no incentive, at the moment, for the armed forces to undertake an asthma study. Such a study might be undertaken at a research institute if anyone was interested and could gain funding.
As for your suggested causative life style, join the club. However Mrs PN says that lack of central heating is not a cause.
The following link and extracts would seem to suggest that cold and damp were not the problems but that atmospheric pollution has a significant effect. Without doubt pollution from hydrocarbons and aerosols has increased dramatically but les visibly than the fossil combustion of the 50s and before.
<<Controlled human exposure studies of acid aerosols suggest increased responses among adolescent asthmatics. Increased ambient and indoor levels of bioaerosols (e.g., house dust mite, fungal spores, endotoxin) have been associated with exacerbation of asthma. . . studies focus on the effects of exposing humans and animal models to a combination of various PM samples (e.g., diesel exhaust particles, oil fly ash) and allergens (e.g., house dust mite, ovalbumin). . . PM exposure can promote allergic sensitization and exacerbate existing asthma . . . Exposure of healthy human volunteers . . . promotes inflammation and increased indices of oxidant formation correlating with the quantity of transition metals in the samples. . . PM promote the formation of reactive oxygen species and subsequent lung injury, inflammation, and airway hyperresponsiveness leading to airflow limitation and symptoms of asthma.>>
The Role of Particulate Matter in Exacerbation of Atopic Asthma