Tech startups are not very comparable to restaurants. Restaurants have limited capacity, limited ability to scale, usually pay rent (so any success can be partially sucked up by the landlord), and have limited times of the day and week to earn most of their money.

To support terrible profit margins (relative to the risk), I also would look at the financial status of restaurant owners/operators, who by and large, aren't in the higher end of the income scale. Almost no one tells their kid to grow up and aspire to be a cook or open their own restaurant (unless they already have a a trust fund).