That is an artifact of NFA 1934.
Before NFA, crew-served weapons were common and inexpensive. Bannermann was selling 1" (25x120mm) Nordenfelt QF Quick Firing) Naval guns by mail order. Right next to various galloper and mountain guns, and even some high-velocity 20mm cannon.
The whole idea that MG & crew-served weapons are "rare" and "expensive" is an artifact of 84 years of NFA, the 50 years of GCA 68, and the 32 years of post-Hughes regulation.
Quite literally, fifty years ago, felons dd not have lifetime prohibitions against gun ownership (except while incarcerated and/or in custody). The US survived more than 170 years without "Prohibited Person" requirements.
This is the insidious nature of infringing regulation. We in the RKBA community have been "conditioned" (for want of a better term) to that "we" constantly have to justify that "we" are law-abiding. Why do gun owners not get a presumption of innocence? Because the laws have enshirned a notion that all ownership is illegal, excepting those narrow definitions permitted under the law.
So, we have been forced to accept a "prior restraint" to exercise our 2nd Amendment rights. Much as we have "accepted" prior restraint on 4th, 5th, 6th Amendment rights as well.
We have been "boxed in" on the 2nd, we are forced to argue about the weapons and not the rights.