Disclosure: My wife is a 3rd party merchant through Amazon's Fulfillment By Amazon (FBA) program. I guess I'm her "CIO".
The online retail space has been evolving over the past couple of years, as we all can tell. Since 1992, when the US Supreme Court ruled that sales tax could not be collected from a state where there was no physical business presence, online retail has operated in an essentially un-taxed environment. You were always supposed to track online sales made to customers in your own state, but there was a competitive advantage over brick & mortar (BM) retail stores. Companies like Amazon could locate their warehouses in Arizona and do business in California without being taxed in California; the Californian citizens were supposed to calculate their tax and remit it on their tax forms. You can probably see that individual citizens wouldn't report this, and the states felt they were losing out on a lot of revenue.
So, the BM stores lobbied the states to implement collection policies; it would become the online retailer's responsibility to collect the sales tax and remit it to the state. Additionally, many states have been changing their nexus laws, such that 3rd party sellers that use Amazon's warehouses to hold their products, a transaction is taxable if it is shipped from a warehouse to a customer in that state, even if the object owner is out of state. This will make online retail less competitive on the pricing side.
But, what BM retail stores forget is that they have a competitive advantage too, they are located closer to the customer at the point of sale. When someone goes into the store, they can check out and walk out of the store with the item in hand (no 2 day wait on getting your item). Additionally, they can impulse shop from the store's inventory. Amazon looks at this and says, if I'm going to be taxes as if I have a physical presence, then I might as well have a physical presence, and they have begun building "micro warehouses" in major cities across the country. Now, you will be able to order online, get the vastly superior inventory storage options that a warehouse provides, and get same-day shipping to the customer, so the customer can have the item in hand by the end of the business day.