My thinking is they (Gov't programs) are incompetent to make it work. Gov't programs can not change gears fast enough to complete the engineering before funding runs out, and we exchange engineering for funding pursuit. When engineering takes a backseat to marketing, there's plenty of opportunity for Feynman's observation about successful technology to creep in:
For a successful technology, reality must take precedence over public relations, for Nature can not be fooled.
SSTO is very hard. The mass ratio is a killer, because after you add the return systems your payload fraction goes to nil. Given, of course, 1990's engineered materials. NASP is an application of the first obvious, air for oxidizer to improve mass ratio. Scramjet and ramjet engines have an extraordinarily high thrust to weight ratio (I've seen claims of 1000:1 for ramjets). But the physics of flying at high speed in atmosphere conspire to create a huge ding in the mass ratio again. It's not a linear relation.It's not optimal for all missions. It's not a one-size-fits-all.
I don't think FR is an adequate debating forum for this, perusing old USENET archives and AIAA papers I can see ample evidence of brighter lights at work on the physics and engineering. If the FEDGOV is going to spend gigabucks on this process I wish they would do it in a way which leverages the efficiencies of capitalism. I will admit I am a fan of TSTO (two stages to orbit). Considering the cost of materials on orbit, I would rather build a space station from discarded rocket boosters than pay to haul them back and forth from orbit over and over again. Lightweight return modules (namely capsules with heat shields) have a plenty good record.
There needs to be an financial incentive to get this going. If we feel it's proper to do as a nation, for Constitutionally supported purposes, then the appropriate thing is for the FEDGOV to get out there and emit the proper perverse incentive, i.e. pay for pound delivered to orbit, pay for person delivered to orbit, pay for surveys, prizes for research and development, etc. Not do the whole enchilada inhouse.
One of the problems from the get-go was that this was supposed to be an X program, meaning a test program to measure things. But to get the AF to sign on, they had to demonstrate a payload bay door. That added thousands of pounds of weight. A 50,000 design ballooned to 500,000, and that was too big. Most of the experts---private and government alike---think they can beat the thrust over drag at lower weights.