How did you form this opinion? Family wealth has almost nothing to do with an individual's financial ability to do a PhD. You don't pay tuition and you receive nominal wages to support yourself. It's not a tech salary, and there's a major opportunity cost for delaying your entry to industry (if you eventually go that route), but that doesn't mean you need a rich benefactor to sponsor you for five or six years.

A PhD is financially viable for anyone who could make ends meet while working at Best Buy. Most people working on a PhD have no family or mortgage.