Since 2008 or so all US government computers on SIPR block USB storage devices are unless they are on an approved list. Autorun is disabled.
Physical security is another big factor, there is a long checklist for a SCIF that at some level takes into account TEMPEST type threats that mitigate many attacks on air gapped systems.
And none of these things are the default on commercial software because users want it to be frictionless. They want software to install right away when you plug in a usb drive, etc.