They are large and heavy. They are only useful for their virtually infinite life. If the military needed it for a few of their bases, they'd contract it out, a few hundred would be built and that's it.

For example a few thousand ISDN adapters were built for the government military. But it lacked corporate support because the Telcos didn't want it cutting into their profits. So ISDN barely existed for consumers. Consumers suffered with 56k modems for 5-10 years until broadband- which telcos sold for more than a phone line, were immune from all the competition requirements of regular phone lines, plus got TV programming profit.