Reliability aside, versatility is the cornerstone of any infantry's standard platform. The LAC is different in that it places heavy emphasis on ranged engagements due to it's exclusively mountainous terrain, meanwhile the LOC has open peaks and ridges, forests, lakes etc that require versatility from your small arms capability. Logistically it's an unnecessary pain to outfit and distribute your units with different platforms and ammunition within the same geographic location, never mind the training. Therefore, the guideline has evolved around the world to adapt the same platform to perform within the deployed AO with some exceptions (again, like the LAC). Example, US troops posted in the middle of nowhere in Afghanistan would most likely use the M16A4 with a magnified optic due to the rocky and open ground for kilometers, while those expected to deploy in more urban terrain or deployed in a FOB outside but still near a city would be using the M4A1 and adapting it accordingly with an ACOG/LPVO and RMR to bring that long-short effectiveness. SIG-716 aside, It makes little sense to deviate into two different platforms on the basis of a standard rifle and carbine. The training and logistics would be and is torturous, especially considering troops don't spend a lot of time down range here. 5.56 x 45mm platforms, especially the AR-15 styled ones are incredibly versatile and user friendly. It's not that there isn't a good 7.62 x 39 platform out there, a modrrnized variant of the VZ.58 would blow the AK out of the water, but that's a pipe dream.