It's part of what NASA does, and it's a very good thing. If commercial companies are left to their own devices when it comes to things like airplanes, very very bad and damaging things happen like unchecked pollutants, urban noise, lack of safety, etc. It's very important for NASA and taxpayers to be a part of this process.
> Supersonic vehicle research addresses the development of tools, technologies, and knowledge to help eliminate today’s technical barriers to practical commercial supersonic flight: sonic boom, fuel efficiency, airport community noise, high-altitude emissions, structural weight and flexibility, airspace operations, and the ability to design future vehicles in an integrated, multidisciplinary manner.