The dealer mark up is his building lease...his family needs.... his food... his clothing... his transportation. You know. What you want to save your money for.
It's probably more for his business expenses, one of which (hopefully) is a salary for himself so that he can take care of those other expenses, which we all have (except the building lease).
All businesses need to make a profit to cover not just their lease, but payroll, insurance, utilities, advertising/marketing, supplies, and so many other things.