Indeed. And I say this as Costco member. There are lot of factors that make Costco memberships work. And a lot of people won't be able to make much benefit out of Costco membership.
I say this as someone who admires their business model and how they treat customers & employees: your typical Costco experience is drive to the suburbs, spend $500 and load up your car with nice to have food products and discretionary purchases. Poorer people cannot do any of these things.