So from a manufacturer profitability perspective it makes no sense.
well that's about as incorrect a statement as you could have typed.

NO warehousing costs, NO manufacturing costs, NO distribution costs.
The 'warehouse' is virtual and takes up a physical space about a cm on a side and 2mm thick.

Not only NO costs to you, but the client who wants the part will pay you to download the file - and with the right digital encryption, you can even decide how many times they can use the file.
The client will even pay for the material to print the virtual part.
And if you're smart you'll colour the parts so that you can even sell them the material to print the viretual part you've just sold to them.

So to sum it up.
A single small setup cost to establish your virtual 'warehouse'. practically no ongoing costs, and the person who wants the part not only pays you for a virtual part but also pays for the materials it's made of.
It's a business wetdream.