Amazon exists in large part because of a tax loophole in existence when web browsers became ubiquitous, where out of state purchases didn't need sales tax. So,

Amazon exists in large part because of a tax loophole in existence when web browsers became ubiquitous, where out of state purchases didn't need sales tax. So, ordering anything not immediately needed and available on Amazon was very likely to have the lowest price. Talk about viral style growth of customer bases!