When the USAF has a very useful ac in the shape of the SR71, it doesn't get rid of it until it has a replacement. The U2 and SR71 used to complement each other despite the latter being intended as a replacement for the former, initially. So why terminate the SR71, unless, of course, there is a replacement!! (I always considered the attempt to bring 3, later reduced to 2, SR71 back into service in 1995 an acknowledgement that the replacement was late or had a problem and was grounded, only for whatever the problem was to be solved sometime in 1997 finally killing the SR71 programmel)
Officially it was the Cost and lots of Pentagon in house wrangling, if memoirs are to be believed, however, cost alone has never stopped the US before.
If rumors are to be believed the replacement, given the name Aurora by some, is plying the skys at this moment and as it will be a properly secret project, they wont have told the press, not even the Guardian.
So maybe 2020 will be the date when the USAF reveals the Aurora, which, incidentally, had been flying since 1997, or thereabouts.
