Walmart alone attracts some 300 million people to its stores each month, and millions more to its website, adding up to more visits than Amazon.com, Facebook or Google get, according to Forrester Research data cited by Bloomberg. “We have a tiny ad business,” Walmart CEO Doug McMillon told investors last October. “It could be bigger.”

Ditto with other major retailers, it seems. While Facebook and Google might know what customers like, only the retailers know what they buy, observers say. “They have a nice story to tell advertisers,” said David Tiltman, head of content at advertising analysis firm WARC, as reported by Bloomberg. “What we see now is a more sophisticated approach to ad sales than retailers have had in the past.”

Retailers are now acting to capture some of this advertising revenue, Bloomberg reports. Walmart has hired marketing-media executives from NBC Universal and CBS. And Kroger has set itself a target of generating about $400 million in additional profit by 2020, some of it to come from such vendors as Unilever and General Mills. Target, too, has attracted numerous vendor clients.

“In an Amazon world,” as Tory Gundelach, formerly with Target and Kroger and now an analyst at Kantar Consulting, told Bloomberg, “retailers have to make money beyond just selling products.”