Where they ever scaled up to "production useful" sizes? Experimentation is one thing, practical application is another. We're talking about two different things.
Regarding the X-59, do you think the sonic boom profile of the X-59 will be the same as the scaled up "production useful" aircraft size?
Again, we're talking about two different things. The experimental researchers can go play all they want, but what they play with won't apply well to full scaled production useful sized aircraft.
The Canadians used a reduced scale model of their CF-105 Arrow and fired it into the upper atmosphere on a rocket to get their supersonic flight data (and they're still searching for it at the bottom of the lake it fell into, since it is one of the only remaining bits of their beloved Arrow program).
The Grumman X-29 was built to test the concept of using a forward-swept wing for high maneuverability and relied on three redundant computers to keep it within its flight envelope (i.e., not crash) it was reasonably successful, but only the Russian Sukhoi Su-47 seem to have used that design.
A reduced scale model will refine and develop the initial concept and allow them to go to the next steps before building a full-scale version. Any idiot that wants to go to a full-scale passenger-carrying prototype without several testing steps in between is asking for disaster.