The quiet supersonic transport is potentially commercially viable, but without a demonstration that the technique actually works in flight, the size and risk of the investment necessary to try it have seemed to be too large for the private sector. (The concept has been out there for a while.)

Another motivation is a desire to understand the design principles and behavior of such concepts at a deep and general level. That's not usually something industry does—often industry's level of analysis and experimentation is just "good enough" to get a job done. If that gets repeated a few times, it leads to both wasted effort and a proliferation of mediocre designs. (As another example, that motivation also drove the National Advisory Committee for Aeronautics—NASA's predecessor agency—to undertake an exhaustive study of airfoils. NASA still undertakes quite a bit of research from a similar perspective.)