None of the X Projects Worked ....
... or they all did ... and they shut them down to cover it all up. (Choose your conspiracy.)
Even then, they were just rockets with small wings.
X33 (Single Stage to Orbit) was a debacle. They made the fuel tank out of gasoline because they couldn't get enough C4 to cure in the shape of a space plane.
Utter stupidity running the show.
At the time, the most plausible story was they aerospace companies were making too much money with the current products. Why introduce a new product that would eliminate all the big dollars coming in? Or, perhaps ... they couldn't do it either. They had never heard of a material called aluminum.
Did the aerospace companies intentionally sabotage the projects? No. They just did what their customer told them to do. Their customer (the NASA) was so incompetent by then, they couldn't design a paper bag if you gave them the paper and they tape.
They were amazing at outreach programs ... damn that's funny. And, they gave out a lot of awards.
Then, we out sourced the whole thing to ... get this ... our enemy ... the RUSSIANS!!!! (Damn, that's funny.) Putin Thanks you for your support.
Bezos and Musk are lighting a candle up the back sides of the US aerospace companies. The dollars have never been in space for those companies (post 60's) ... so ... they will likely stay in the "fight more wars" business and let the rockets go.
Bezos and Musk know how to make a buck ... they won't be worried about the golf show unless they can sell shoes and pins. My guess is they'll haul back chunks of silver and lithium.