The military doesn't always get what it wants
Off hand, the A-12 "Avenger II" (AKA "Flying Dorito Chip") and its proposed replacement, the A-X
Let's not forget the M247 DIVAD "Sergeant York", either. It was a high-priority weapons system that ended up being cancelled during development because they didn't work properly despite being built from off-the-shelf components.
There was also the P-7 ASW aircraft and the AH-56 Cheyenne attack helicopter.
I'm sure there are other examples, like the XB-70A and a lot of projects that probably never got past the paper or mockup stage.