> I mean, so long as the person didn’t die of infectious disease their remains could probably be recycled in to the biosphere?

Human bodies are full of parasites and pathogens that are dangerous to humans: just because someone got hit by a car doesn't make their body sterile. That's one reason the BSE (mad cow disease) spread, feeding cows to other cows. It's also a reason we don't generally fertilize crops with human waste, although horse or cow manure works very well.

So we probably can recycle human bodies, but there are extra genuine health concerns. One pretty safe way is to bury them in the ground and let them get eaten by worms - but as the article points out, even that comes with health risks.

If I recall correctly the BSE outbreak was due to using brains in feed.

I agree with your general point about extra genuine health concerns.

> feeding [components of] cows to other cows.

How did the Japanese do it with night soil then? Did they burn it before using it as fertilizer?

I don't know about the Japanese, but in Europe where this practice was common (certainly in London) one answer is simply that they tolerated more outbreaks of infectious disease.

It's possible to make it safe through composting, but that requires more time and skill than a typical compost heap. Most composting authorities recommend keeping cat and dog faeces - less dangerous than human waste, but much worse than cow manure - out of the garden compost heap.

Having a more or less vegetarian diet helps it some at least - less trophic layers since the diet is more akin to other herbivores although not as fibrous as grazers. Since fish was far less spread before advances in refrigeration and transportation those inland more would have been more subsidence farmer involuntarily vegan - let alone the increased acceptance of meat.

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.