The real problem was noise. Everything was predicated on being able to do cross-continent mach 1+ flights. When the US then Europe closed off faster-than-soun

The real problem was noise. Everything was predicated on being able to do cross-continent mach 1+ flights. When the US then Europe closed off faster-than-sound flights over land, that was it. After that, it couldn't make money. Then everything else started to become more significant and you could see the writing on the wall.