Why? Because we buy 'em regardless so why should they take any more care? Would it sell more reps? Probably not. It's kinda like complaining that your local speed cook isn't producing lab quality dextroamphetamine, he doesn't care as the shit still sells.
Also of cause last time I looked speed was decidedly more expensive than legally obtained medical amphetamines. It's the cost folk tend to add when they face life in prison or being stood against a wall and shot as happened to a couple of fake bag makers in SZ last year.