The list of advantages for F/T is plentiful, so to keep it short, there are absolutely no advantages, except disadvantages of Live feeders, not a single advantage that could convince someone to switch over.
One common thing you hear with owners who do Live which is totally wrong is, "I want the snake to feel like it's still in the wild, its better for it", they still attack the F/T feeder the same way, so it's no different.
A bad breeder might feed live because it may be easier on them, too cheap to invest in a humane way to kill the mice/rats so they just feed them as is.
Also, you'll find from many veterans on here, they don't believe in a snake that only eats Live or won't eat F/T, every snake can be switched over with time, skill and patience.