Probably the biggest reason that buffs are easy kills, is that most interceptors are highly determined, and the fear of being shot down will not deterr them in their attempt to shoot a buff down.
I've seen all sorts of pilots, the good and bad. The good pilots shoot down buffs easily. The bad pilots have it more tough, but still they shoot down buffs anyway.
They don't care if they are bleeding, radiator busted, oil splattered, flap torn, elevator nuked, aileron snipped, etc etc.. as long as the buff is ahead, dead 6 or not, in most cases they will follow it and shoot at it until the ammo is all spent.
2~3 of such guys around and most every buff formations is practically toast. They jump at it like moth to a flame, guns blazing.
However, if one is trying to actually stay alive, and shoot down buffs at the same time, it's actually not very easy.
It's easy if you already have 5~6k alt over him, but in many cases buffs are already within 10 mile range of its target, less than a minute away from dropping point when they are spotted, usually by people who are flying lower than them.
In such case, you don't have enough time to grab altitude as leisurely as you please(unless you don't care whether he busts all your FHs or not). You have to catch up to him, and start high-risk attacks.. swerving and ducking a lot, weaving through gunfire, popping a shot here and there, all the while trying to shoot him down before he makes the drop.
Bur if you don't care about being damaged, you just approach his six, go straight with guns blazing. The chances are the buff guns will knock you dead, but you'll also probably down one buff. 2~3 same type of guys nearby, and the buffs are practically dead.
ps) ofcourse, this can alternately translate into the fact that most buffs are usually flying pitifully low. In the MA, a buff comes in 18k+ and usually he'll be going home unscathed.
A buff's best pal is alt. His best chance of success is to not meet interceptors at all. Flying at an alt where you can expect to meet interceptors, and then complaining that the buffs are too easy to be shot down in presence of them, is basically nonsense.
Interceptors are SUPPOSED to shoot buffs down. That's why buffs flew in numbers, and with escorts.