This was low skill manual labor. When I was in the Army in the early 1960s there were several men in my Army unit who worked in service stations. They weren't very bright and had limited skills.
It is my opinion, that steady increases in the minimum wage, pushed by labor unions and the Democratic party have created a large pool of unemployed people who are unemployable at current minimum wage levels. Unemployable all their lives. I knew those guys.
The Japanese government has a policy that subsidizes small businesses. The Japanese reason is that small businesses employ the low end of the Bell curve of employment skills.
I think the evidence supports that position and minimum wage laws create general unemployment, particularly higher unemployment among blacks and young people.