Costco attracts people who ascribe a very low value to their own time, just look at the 20+ car lines to save a few bucks on gas. It’s no surprise that type of customer tolerates a line to have their receipt checked.
Have you been in a Costco, or is your primary interaction the gas lines? I guess the receipt line every once in a while takes more than 30 seconds? I can’t think of anything else inside that at all is a tax on my time compared to a normal grocery store.