Many of the people eating in Costco have children with them. People with a lot of children buy in bulk.
It’s their gasoline prices that I find amazing - fifty cents a gallon cheaper. If you use their credit card it’s even cheaper than that.
See, I’m a Costco member, but I don’t bother with the gasoline. Why? Because at the Costcos in my area, the gas lines are always so damned long. Yes, their gas is usually signficantly cheaper than the local average, but I find that if use GasBuddy.com or other similar, I can find other local stations with prices comparable to Costco’s or perhaps only $0.05 more per gallon... and no lines. If I’m buying say 12 gallons, it makes sense to go to that other station. Saving $0.60 total by waiting around at Costco just isn’t worth it.