Here are three explanations for the recent demise of America’s storefronts.

1. People are simply buying more stuff online than they used to.

The simplest explanation for the demise of brick-and-mortar shops is that Amazon is eating retail. Between 2010 and last year, Amazon’s sales in North America quintupled from $16 billion to $80 billion. Sears’ revenue last year was about $22 billion, so you could say Amazon has grown by three Sears in six years. Even more remarkable, according to several reports, half of all U.S. households are now Amazon Prime subscribers.

But the full story is bigger than Amazon. Online shopping has done well for a long time in media and entertainment categories, like books and music. But easy return policies have made online shopping cheap, easy, and risk-free for consumers in apparel, which is now the largest e-commerce category. The success of start-ups like Casper, Bonobos, and Warby Parker (in beds, clothes, and glasses, respectively) has forced physical-store retailers to offer similar deals and convenience online.

What’s more, mobile shopping, once an agonizing experience of typing private credit-card digits in between pop-up ads, is getting easier thanks to apps and mobile wallets. Since 2010, mobile commerce has grown from 2 percent of digital spending to 20 percent.

The Growth of Mobile Shopping

Cowen and Company

People used to make several trips to a store before buying an expensive item like a couch. They would go once to browse options, again to narrow down their favorites, and again to finally pull the trigger on a blue velvet love seat. On each trip, they were likely to make lots of other small purchases as they wandered around. But today many consumers can do all their prep online, which means less ambling through shopping centers and less making incidental purchases at adjacent stores (“I’m tired, let’s go home … oh wait, there’s a DSW right there, I need new sneakers”).

There will always be a place for stores. People like surveying glitzy showrooms and running their fingers over soft fabrics. But the rise of e-commerce not only moves individual sales online, but also builds new shopping habits, so that consumers gradually see the living room couch as a good-enough replacement for their local mall.

2. America built way too many malls.

There are about 1,200 malls in America today. In a decade, there might be about 900. That’s not quite the “the death of malls.” But it is decline, and it is inevitable.

The number of malls in the U.S. grew more than twice as fast as the population between 1970 and 2015, according to Cowen and Company’s research analysts. By one measure of consumerist plentitude—shopping center “gross leasable area”—the U.S. has 40 percent more shopping space per capita than Canada, five times more the the U.K., and 10 times more than Germany. So it’s no surprise that the Great Recession provided such a devastating blow: Mall visits declined 50 percent between 2010 and 2013, according to the real-estate research firm Cushman and Wakefield, and they've kept falling every year since.