> but I have never been able to find a clear answer for /why/ those processes are incompatible.
You can't find an explanation why they're different for the same reason you can't find an explanation why writing poetry and riding a unicycle isn't the same process.
Or, you could look at your peer answers where people very much do provide a non hand-wave answers. Chip fabrication isn't undergrad philosophy; there are well understood reasons for why things are done if you care to find and understand them. And there are stakes in the millions or billions of US$ for getting them wrong.