Damage control. Whether it's temporary or long-term, right now there is a lot less variety of items shipped and sold by Amazon or fulfilled by Amazon.
If they continue to follow through on this move they offload a lot of risk onto sellers. Even if they reverse, it's already made a credible threat to wholesalers and shippers that can be used to extract lower pricing. Either way Amazon wins, and they can afford to lose money for a very long time waiting for the results to play out.