What is the whole point of this exercise? Amazon gets nothing from the dealers, and Amazon is certainly not offering Prime 1-2 day free shipping on this, so why would a Hyundai dealer bother listing their lot inventory on Amazon AND their own website?
Only thing I can figure is that it will help boost their sales of Hyundai after-market accessories from the third-party sellers who list them there.
Going direct would seem inevitable for all automakers since they have to combat the new gorilla in the room, Tesla. Tesla is more efficient in making cars aka gigacasting, more reliable with less maintenance aka no oils, only electrical which leads to higher margins. Plus add on top of that, that they sell direct to consumers so cutting out the expensive middle man, it's inevitable that other automakers have to follow suit.