I see now that "blanket ban" is an incorrect description. As I understand it, the current prohibition is that supersonic planes (except Concorde) are allowed, so long as they are below a given noise level. Here's the law,
https://www.law.cornell.edu/cfr/text/14/91.821 :
> Except for Concorde airplanes having flight time before January 1, 1980, no person may operate in the United States, a civil supersonic airplane that does not comply with Stage 2 noise limits of part 36 in effect on October 13, 1977, using applicable trade-off provisions.
Going back to an article from 1973, at http://elr.info/news-analysis/3/10067/faa-promulgates-strict... :
> The policy underlying this regulation puts the burden of establishing the environmental acceptability of supersonic civil aircraft flight on the proponent, rather than on the affected public. However, the FAA has also made available reasonable opportunity for aircraft manufacturers to prove the environmental acceptability of supersonic flight if they are able to control sonic boom research without harmful effects on the public.
The problem appears to be that airplane manufacturers cannot meet the existing noise level, so instead want the FAA to say what higher level is allowed. This places the cost and responsibility on the government rather than the manufacturers. So of course the manufacturers would like to shift that expense to someone else.