The LMG is used with the long burst to suppress the enemy and keep them back, good for covering a retreat or heralding a charge. It's a support weapon to be used with a team, so it goes to team antags. Not for solo traitors, so it wouldn't be chosen over the traitor gun.
As for the bulldog/bullpup, well, everyone knows the shotgun meta will eventually be nerfed to ass, so people will start exploring new options. This could be one of said options, a semi-auto rifle to be used instead of the burst rifles. Make it notably cheaper than the bullpup and bulldog and it'd get attention.