Amazon is worried about getting sued because they're a fulfillment and 3rd party sales service rather than a traditional business who owns most of their own inventory. If I'm sitting in Nebraska selling Beanie Babies that I'm drop-shipping from AliExpress in China, and someone in South Dakota is selling the same Beanie Babies, also on Amazon, and someone in Nebraska buys one of said Beanie Babies from Amazon, the NE Attorney General is inclined to say Amazon has a "presence" in the state (me) and should be withholding taxes, even if the merchant who fulfills the order is in South Dakota. These lawsuits were brewing in several states already so Amazon just took the proactive step to implement it before the lawsuits came to fruition because it was cheaper than waiting for the suits, since the costs will be borne by the merchants and not by Amazon. Amazon is not a "good corporate citizen", they are just looking out for their own bottom line.