Yes but these businesses have been around for a long old time usually.... I'd not expect to see tiny profits on the capital they have in premises, stock, tooling etc. If I had 3 million in capital, I'd want to see it work harder than returning percentages I could get safely and predictably with a financial product on my capital.
Probably though, second hand car retail is just a small element of their business. New cars and service (particularly service) will be where the real money is.
I'd expect a used car only sales operation to be slim pickings.