This actually takes more time than the old way...
So rather than having a shortened URL pointing to the product page and clicking on the 1-click buy button, now you have to actually type out '#amazonCart" to buy something, which is a full 10 more button presses than the old way. Plus your purchase history is now public (something you could have done the old way too by using the social share buttons on the confirmation page, which ironically enough would have taken less button presses to do anyway).
So tell me, why would anyone do this?