A tech demo is not a fully fleshed out anything. It's just there to do as the name says. If it ends up being used, great! But there's a lot of concept trailers that go literally nowhere. The point is to show off, not be a "Confirmed!" kind of thing. Remember that awesome game Agni's Philosophy? Of course you don't because it's just a tech demo.
https://www.youtube.com/watch?v=UVX0OUO9ptU