In this context, “generic mini-PC” doesn’t need to even be “non-gaming-PC”, just not a platform for buying Valve’s games; a razor-and-blades model requires that you be the one selling the blades. If someone just goes and runs games purchased from GOG, that’s already an issue for them.

It’s why inkjet printer manufacturers, who do use this model, try to make it so stupendously difficult to use ink from competitors (outside of the bottled-ink printers, which don’t use that model, where the manufacturers are fine with you doing that).