Bomber jackets were a major part of military life, but following the Korean War, and especially after the Vietnam War, the MA-1 was integrated into civilian life. While the jacket was obviously for U.S. military personnel, the jacket quickly (and more easily) spread to a non-military audience. Much like the pilots who wore the jacket in an era when planes didn't have closed cockpits, normal individuals could enjoy the warming qualities that are built into the jacket. Traditionally constructed bomber jackets work in a temperature range that goes from roughly 14 to 50 degrees Fahrenheit, so the style was much desired for those who happened to need a functional jacket that could be worn ideally from autumn until the middle of spring.
Of course, in the switch from combat to civilian use, changes were made to the jacket. Notably, the wool collar and cuffs were changed to an acrylic knit (with more time in home storage, insects were known to eat at the wool). There was a switch to a non-quilted liner, and certain manufacturers applied extra water repellent treatments for those in wetter environments.
Police departments have even added the MA-1 to their uniform, especially for those who live and work in outdoor temperatures that are exceptionally cold. To put it simply, the bomber jacket wasn't just for pilots anymore, and was simplified for other tasks, but became popular for its lightweight body and simultaneous cold weather functionality.