It doesn’t. Composting and burying leaves for example aren’t the same thing.

Composting provides extra oxygen and whatever other steps are necessary to accelerate the decomposition process.

A buried body can last many years, especially if it’s several feet into the clay layer.

Try it. Bury a cat or dog six feet under and come back in five years. If it’s common clay, a large percentage will still be there.

> A buried body can last many years, especially if it’s several feet into the clay layer.

And in some cases (e.g. peat) "many" can end up being "hundreds" or even "thousands".

Sorry, I was unclear: I meant “much the same thing on the timescales at which buried humans are likely to be disturbed”, so 50-100 years at a minimum.

I imagine it will be at least that long, and likely much longer, until the land used for cemeteries is repurposed.

This feels like snake oil. A grave without cremation has to be way less energy consuming than controlled "compostation".

The difference is that you can't bury a body in a garden, for example (for sanitary reasons). But after it is properly composted, what you have is, well, compost. Which can then be placed somewhere and a tree planted in it, for example - and then you have a living gravestone.