My theory: apparently a lot of companies use the IP-addresses internally. And apparently the intention was to sell the IP-addresses already for a long time. But buyers would be faced with a lot of traffic coming from all those companies using the ranges internally, instant DDoS. Maybe this is an attempt to "clean" the IP-addresses before selling them. It will probably only take time before most companies using the ranges internally and having problems now (or happily continuing business now with the help of Pentagon servers), to reconfigure their networks to fix it. In the meantime the Pentagon can probably collect some interesting traffic, speeding up the whole process of reconfiguration by companies who use the ranges, to prevent their secrets from falling into exactly the right hands.