Im just guessing but I feel certain it is because of 6 man crews vs 4 man crews. Because all 4 man crews do it.
I'm pretty sure it's the way the Maxim is coded compared to the other HMGs. Maxim's the only one whose minimap icon that has three arms coming out of a circle like AT guns while other HMGs are just dots, and it is the only one where losing a crew member requires another to walk up to it to take over moving it like AT guns. I always imagined it was intentional off that (but I still fucking hated it).