It's a pretty brilliant business model, I think.
First, it takes people a while to figure out they only need one order for 2-3 people, so they still get a ton of those extra orders.
Customers mistakenly paying more than they needed to is not sustainable revenue for a business. It produces higher revenue in the beginning stages of the business location, but eventually that revenue needs to be replaced in later stages or else the business collapses.
Take the self serve frozen yogurt stores for example. When they open up, people go in and fill up that HUGE cup with yogurt and toppings and then gasp when they have to pay $8 to $10 bucks for it. When all your customers are new, a lot of them do that, and it produces a TON of revenue for them in the first year. Yet now a good chunk of the stores in the industry are closing or are for sale because customers don't continue doing that. The customers now make $2, $3, and $4 cups instead, and the business as a result only has a fraction of the revenue and can't pay the rent and utilities anymore.
I don't think that is a brilliant business model at all. It's a temporary boost of revenue, and nothing more. I think a lot of Five Guys franchisees are going to be following the self serve frozen yogurt store business owners in the for sale/closings.