The ban was specifically to hinder the Concorde, so it made sense to base it on supersonic flight rather than noise in case the Concorde would have managed to mitigate its noise level one way or another.
Reference? There was an "Anti-Cordorde Project" [1] but its purpose was to ban all supersonic flight, for environmental reasons. Concorde being the only in regular service, thus the targeted name.
Reference? There was an "Anti-Cordorde Project" [1] but its purpose was to ban all supersonic flight, for environmental reasons. Concorde being the only in regular service, thus the targeted name.
[1] https://en.wikipedia.org/wiki/Anti-Concorde_Project