As I explained...it is not practical or useful in combat. The
range is too short, reloading is too slow, too few rounds can be
carried.
Most combat takes place at beyond 100m range, shooting each other
with assault rifles...if you carry shotgun for infantry warfare,
you shoot hit nothing, only attract enemy to fire at you.
For urban warfare, automatic fire is preferred, more accurate and
less likely for civilian casualty.
Most armed forces do not have shotgunners....I think you play too
much CS.
Shotgun in SAF have...but for protection of installations (mainly
at Jurong Island), for the specific purpose to bring down
terrorists at close range. That's all. Even then, they're still
partnered with someone carrying a SAR-21.