I think it's mostly affordability. They are also very reliable. That said I've looked off and on for a cheap old beater 12ga A5 Browning over the years. Haven't found one cheap enough, everybody seems to think they are ALL collectable. My idea is to cut it down in the stock about 3" and put a pad on it. Then chop the barrel to 18" and get an extended tube for it made. Clyde Barrow was murdering scum but he did know his weapons.
Like a Rhodesian FN A5. http://john1911.com/cleaning-the-rhodesian-a5-shotgun/