You are being sarcastic here, but ironically you are not far from the truth. The core financial model of a businesses is not always obvious.
McDonald’s is a real-estate business. Costco is a subscription business.
I don’t think that’s accurate. The membership fee is a trivially small percentage for most members, and can’t be a significant margin driver. Especially for those members who have a pack of kids and shop Costco regularly, spending hundreds of dollars per visit.
I personally think the membership fee exists as a gating function to keep less-prolific customers out of overcrowded stores on weekends.
Their margin comes from subscriptions.