Why doesn't the US military use Glocks?
I'll throw my hat into the ring. Here are two possibilities:
1) it takes about 30 years for a design to be accepted as 'mil spec'
2) Glocks are more subject to 'limp wrist' failure to cycle, other designs (1911, P226, M9) are nearly immune to this
Ex - Navy, Persian Gulf Veteran. Loved shooting the M14, 1911, M60, M2