British e-tailer Overclockers UK was the first to shed some light on the matter. The retailer claims AMD is no longer offering the $499 standalone Radeon RX Vega 64 video cards. OCUK's purchasing manager clarifies was a special launch offer that only lasted for a couple of hours because supply sold out a lot faster than expected. The only RX Vega 64 cards that are still supplied by AMD and its partners are the $599 packs - which include "free" copies of Wolfenstein II and Prey.
Dutch tech site Hardware.info heard from AMD's two largest add-in board partners that the $499 launch price was far from realistic. The article backs up the claim from OCUK that the higher pricing of Radeon RX Vega 64 is not caused by the traditional retailer price gouging. Pricing is higher than the promised $499 price from AMD because it is simply impossible to build and sell the cards for this price.
Basically, AMD is charging too much money for Vega which makes it impossible for the supply chain to sell the cards at the promised launch price. Hardware.Info heard the $499 price can not be achieved without the add-in board card maker, the distributor, and the webshop selling the cards at a loss. The cards have to be sold at a price about $100 (100EUR) above the $499 "launch price" to achieve normal margins.
If you're waiting for the Radeon RX Vega 56, be prepared to pay $100/100EUR more than the "$399 launch price" because this card is reportedly hit by the same issue.