It used to be that if you wanted a military jacket, you went to your military surplus store and bought one. The prices ranged depending on the age of the coat and whether it qualified for historical re-enactment, but you pretty much wore it because you wanted something more durable than fashion’s attention span. Actual military and camping types go for them, as do members of the punk and goth movement, since most of what forms that aesthetic comes from a certain post-apocalyptic appreciation where sewing skills and secondhand would thrive.
I’m bemused by the fashion takes on them, and I’m opting to blame them on the rising popularity of Captain Jack Harkness. Every character he encounters has to comment on his WWII Brit military coat. It sticks. I wouldn’t be surprised if a few fatshionistas also wanted a piece of that admiration. Even without it, the interpretations entertain me – military seems to cover everything from “equestrian” to “double button.”