Seems like a lot of lost time during magazine changes. Full auto is so you can send a lot of rounds down range quickly. Can’t do that if you are changing mags all the time. Might as well have stuck to the full auto M16’s.
It would be for the caliber. A BAR at least had the oomph to hurt something, despite the mag fed disability. But I am a bit old school, having carried the M-60 (with ALL its problems, at least it put a world of hurt downrange). It would deny the enemy the ground in front of it. And that is the point of a light machinegun.