I think it has more to do with the employment situations in those states. Maine employment of young men is low, while North Dakota has jobs available out the Wazoo. I know when I graduated from high school in Maine, nearly my whole class went into the service.
Same with my high school in Maine.
I remember 99% of my senior class took the ASVAB test. A huge number joined the service.
I learned later a number of them stayed in until retirement.