Vladof ARs hard to find

Why is it so difficult to find a decent vladof AR? Over the course of my two playthroughs, I’ve found tons of vladof pistols and snipers–none of which I’ll ever use–but finding a common rifle is about as rare as finding a legendary. I’ll find plenty of Torgue, Dahl, COV, and Atlas rifles, but it seems like vladof ARs are rated to drop a lot less frequently. I would very much like to find a good dual spingun, but that seems impossible with the drop rate seemingly geared towards not dropping vladof rifles.