It seems like it would have been wise to keep enough of the production capabilities to where in a pinch production could have began without having to rebuild all the necessary machinery, molding, etc, to start production again. I don't know why it was done.
Political arrogance and bureaucratic pettiness. It's a way to insure that "their" decision can't be undone or reversed by a change in agency management or political regime. I'm certain if you asked, however, they'd give you all sorts of accounting gibberish and BS logistical cost/benefit arguments.
The same thing was done with the tooling for the SR-71 Blackbird, I believe, and whoever made that decision should have their butt kicked.
I don't know about the SR-71, but IIRC, its was McNamara that ordered the Tomcat tools & jigs destroyed.