Trophic layers are a decent reason why. Apex predators of all sorts tend to collect pollutants for little energy gain. If you let say crows feed upon human flesh that is perfectly fine since they can't really prey upon humans but if you let say big cats, bears, wolves or wild dogs feed upon them they start to view humans a food source and can get it - although not without heavy consequences. Maneaters usually have teeth so bad that they essentially go for humans as their equivalent of "soft foods" despite the danger we are as frankly comparably abominations even by standards of apex predators.

Not to mention other incentive reasons - turning human remains into profit makes for bad incentives for the living. Instead of just leaving them to rot completely they end up being a public health risk, upsetting families with grave robbery, and possible murder for the sake of profit. There is a reason why the medical profession switched to plastic and it isn't because plastic of a perfectly anatomical match is less expensive.