"It's a very simple reason," Kniffen said. "It [would give Amazon] a nice little halo."
Kohl's roughly 1,100 department stores across the country — most of which are only one level, are detached from malls and have plenty of parking space — would help grow the internet giant's physical footprint, he said.
Earlier this year, , where it now sells some of Amazon's tech gadgets and accepts Amazon returns at a handful of stores.
The Wisconsin-based department store chain has quietly been working on an alliance with Amazon since the spring, Kohl's chief merchandising and customer officer, Michelle Gass, told CNBC when the partnership went live. Gass will be succeeding Kohl's CEO Kevin Mansell in May, when he retires.
"We've got a really simple objective ... to improve traffic in our stores," Mansell told CNBC Wednesday about the relationship. "The objective right now is to improve traffic, which would lead to an expansion of the program."
Mansell wouldn't comment on Amazon acquiring Kohl's.
The "early indications" from the Amazon pilot, which is only a few weeks in, are "very positive," Mansell said.
Amazon should outright own Kohl's, as it would give the company a place to sell and store merchandise, and accept returns, Kniffen said. This opinion is held by other retail industry analysts.
"Four hundred Whole Foods stores isn't going to do that for them," he said. And Kohl's $7.5 billion market capitalization would only be "pocket change" for Amazon.