The top three fast food franchises for yearly U.S. sales, according to the 2018 QSR Magazine Report, which breaks down sales numbers from the previous year, were McDonald’s, Starbucks and Subway. Here’s how the numbers shook out:

1. McDonald’s -- 14,036 units, $37,480,670,000 in sales, or $2,670,320 in sales per unit.
2. Starbucks -- 13,930 units, $13,167,610,000 in sales, or $945,270 in sales per unit.
3. Subway -- 25,908 units, $10,800,000,000 in sales, or $416,860 in sales per unit.

Now, if you were starting your own business, you’d be pretty happy with any of those numbers. The worst of them, Subway, is reeling in nearly $11 billion in sales each year.

Related: 5 Things You Need to Know Before Investing in a Chick-fil-A Franchise

Chick-fil-A was ranked a not-too-shabby eighth by QSR, after taking in $9 billion in sales. That number trailed Burger King, Taco Bell, Wendy’s and Dunkin’ Donuts in addition to the top three.

But, the most amazing part of this is that Chick-fil-A only operates 2,225 restaurants. That’s less than one-sixth as many as the top-three earning restaurants -- less than half as many as the rest of the franchises ahead of it. Of the top-50 earning restaurants, Chick-fil-A ranked 21st in the number of units.

So, how did Chick-fil-A rank so highly in total U.S. sales? By earning more per store than any other restaurant. A lot more. In fact, the average Chick-fil-A unit made around $4,090,900 in 2017. By contrast, the total sales for a McDonald’s ($2,670,320 per unit), Starbucks ($945,270) and Subway ($416,860) is $4,032,450.

Related: 24 Interesting Facts You Should Know About Chick-fil-A

That’s crazy -- especially since Chick-fil-A is closed on Sundays.

Most people would assume that closing one day per week could hurt company profits. However, it’s clear by the per-unit sales numbers that something about Chick-fil-A makes it more attractive than its competitors. Could it be that closing its doors one day a week actually helps Chick-fil-A make more money, not less? Here are three reasons why that might be the case.

1. Closing creates a craving. It’s like the old saying: “You never know what you have until it’s gone,” and sometimes, when you want Chick-fil-A on a Sunday and can’t have it, it only makes you more likely to get it on Monday.
2. It helps attract better employees. When S. Truett Cathy founded Chick-fil-A, he wanted employees who would stick around for the long haul. According to a piece in The Washington Post, Cathy used to tell applicants, "If you don't intend to be here for life, you needn't apply." By allowing employees to have a day off -- to go to church or an NFL game or simply live their lives -- Chick-fil-A can create a healthier environment and provide better service to its customers.
3. Its customers appreciate the mindfulness. While many customers find Chick-fil-A problematic due to Chairman Dan Cathy’s stance on same-sex marriage, many others also appreciate that the company gives its workers a break. As S. Truett Cathy once said, “We aren't really in the chicken business, we are in the people's business.”

Related: You Can't Own a Chick-fil-A Franchise. Here Are 3 Solid Alternatives.

Perhaps Chick-fil-A is as popular as it is because it has food that customers like, has chosen good leadership or has a good marketing team. Maybe it has little to do with being closed once a week. But, based on the numbers, it sure doesn’t seem to hurt.