Doctors follow trends in diagnosis, depending which drug the pharmaceutical companies are pushing.
That isn't the point. There are probably a higher percentage of asthma sufferers because diagnos is better.
However the odd thing is how many supposed asthmatics make the grade in athletics, swimming and cycling compared to previously. And how many of them have asthmatic events requiring medications which can give an advantage just before events. And, despite every minute detail of their performance figures being recorded end up with medical records going astray or not treatment not recorded.