I don't imagine the USAF had much option.
For whatever reason the aircraft suffered a number of incidents and accidents. The cause of those is irrelevant - the USAF (rightly or wrongly) seems to have declared the aircraft unsafe.
To spend $ lots on fixing the alleged problems, then selling the aircraft would have been one option, but to sell them 'as seen' would have given the absurd, money-grabbing American lawyers carte blanche to sue for the slightest problem at the hands of their new owners....
You can blame the destruction of these aircraft on the ridiculous American litigation-culture (surely an oxymoron) - and the risk to the USAF posed by blood-sucking lawyers.