Because technology is in service of individual and consumer needs. If there isn't a sustainable business model for supersonic passenger flight then it doesn't exist. And, frankly, it's not up to government to provide that.
Technology is both economics and engineering. Just because something can be done, doesn't mean it should be done if no one is willing to cover the costs.
There is another thesis that technology no longer disappears anymore. It will remain in some dormant form. Some crazy hobbyist group in the US, Europe, or Japan will lovingly curate it. Even now, I think you can charter the operation of a restored supersonic aircraft, if you have enough cash. Not sure if any have an extra seat for a passenger, though.
Technology is both economics and engineering. Just because something can be done, doesn't mean it should be done if no one is willing to cover the costs.