The real reason celebrities show up to Wal-Mart's shareholders meeting

Reese Witherspoon stood before thousands of screaming Wal-Mart workers Friday and led a "USA" chant at the company's annual shareholders meeting.

She spoke lovingly of the world's largest retailer, saying Wal-Mart is "redefining retail" and delivering "miracles" to mothers all across the country with services like click-and-collect grocery shopping.

Witherspoon, who was the host of Friday's event in Fayetteville, Arkansas, wasn't paid for her appearance. Musicians Mariah Carey, Rod Stewart, Brian McKnight, and Ricky Martin also performed free of cost at the annual meeting.

These stars usually command six-figure payments for performances and appearances. So what's in it for them?

"Every entertainer that is here has something to do with our business," Wal-Mart spokesperson Dianna Gee told MSNBC during the equally star-studded event in 2013. "There's some connection from the business, whether it's CDs, books, or t-shirts." Film studios and record labels "really work with us" to recruit the performers, she added.

Her explanation makes sense. As one of the world's largest retailers, Wal-Mart has access to 35 million shoppers daily.

If the company decides to feature a DVD or album, sales of those items could spike.

A Wal-Mart spokesman confirmed to Business Insider last year none of the celebrities are paid for their appearances at the annual meeting.

Musicians Pharrell Williams, Robin Thicke, Sarah McLaughlin, Aloe Blacc and Harry Connick Jr. performed last year. Two years ago, celebrity guests included Kelly Clarkson, Jennifer Hudson, John Legend, Tom Cruise, and Hugh Jackman.

This year's event drew about 14,000 people, including workers and shareholders, from around the world.

The meeting is mostly a pep rally of sorts, with celebrity performances punctuated by speeches from Wal-Mart executives on their plans for the future of the company.