Even once you achieve post scarcity, post scarcity only applies to fungible goods. Everyone can have an amazing computer, a 500inch TV, a big upscale house, their own Tesla, and an entire team of robot servants. All those things are fungible. The only question is of resources/assembly, and automation can make that free, or so cheap as to not make a difference.
Not everyone can have a small seaside cottage on the east coast of Nantucket, or right on Venice beach. There is only so much room for small cottages in a particular desirable location.
Only one person can have the original Portrait of Jan Six by Rembrandt. Even if you can make a perfect molecular copy, there will only ever be one original.
Because people will want to own/access things with natural scarcity it will be necessary to have a system for allocating naturally scarce resources. We can come up with some complex merit based system that will inevitably lead to stupid results and rampant corruption, or we can keep going with the only system that has been shown to work, the free market.
Of course people who don't already own naturally scarce resources will want to be able to purchase them too, and so they will create artificial scarcity. Maybe your state of the art new car costs a few hundred dollars, to pay the designers and researchers who invested their time in the research and design that made it possible. Maybe some shows/games/VR whatevers cost a bit of money.
And guess what, we will think its a wonderful improvement. Every single human on earth will live as well or better than the middle class in the richest countries do now, WITHOUT needing to work at all. Everyone will have the choice: A) live a fine life, and do nothing but pursue pleasure. B) live a fine life, work in a creative field, and give away your works because you think things should be shared, or you just like giving stuff to the world. C) Work hard to get access to the top tier of luxury, while selling your work product. In a world where A and B are totally viable options, why try to come up with a reason not to have C.