a.) In heavy forest/jungle you can't see the target but you still have to suppress them, so high volumes of fire across broad arcs is merited. The physics of dispersion means this will only work at pretty close range.
I haven't fought in the jungle, but I've been in some very tight patches of veg in Thailand, so I understand the dynamics of old and juvenile growth in the bush...

Why do we presume that we can't see the target? Didn't the enemy sight their target before opening fire?