actually most franchise restaurants are not profitable and eventually go out of business. subway is famous for being basically a pyramid scheme that only makes money by fleecing aspiring restaurateurs. mcdonald's is an exception because they are primarily a real estate company and commercial landlord.

Most things go out of business. That's why the franchising model exists. Local owners know their local market best and they take a calculated risk on it.

From what I understand, McDonald's franchisees can make 5-15% of gross revenue of their location. That's a decent return, along the lines of other investments. As with all investments, you may lose too.