When the law was enacted in Maine many many moons ago, I think it was a necessary thing because money was more of an object than it is today and family members were headed into the woods with anything that would shoot.
I know this for fact because with my Dad and four of us boys living in a two room shack, guns were hard to come by. We had a .30-.30 Winchester my Dad bought for $7.00 and a haircut (he moomlighted as a barber for a while), an ancient 12 gauge single shot, a .22 single shot, and when I became old enough to hunt alone, between my Dad and me we bought an old British .303 for $15.00 (By the way, I still have every one of them too).
So we carried what we had and hoped for the best. I shot several times at deer with the .22. I never killed one but I slowed him down so my Dad could finish him with the old saddle rifle.