At the time the cards were expensive as we were tipping into the 4k realm, but the idea showed promise and set up the idea that 2-3 cheap cards could be linked to give equal/slightly less power than cards 5x the price. This backed Nvidia into a corner; why buy a new card when you can raid the second-hand market - the revenue of which Nvidia sees none?
Nvidia have stated that their market is high-end GPUs. Offering software solutions to hardware constraints, in this case, price, is at odds with their business strategy.
OTOH, AMD have said they will focus on offering mid-ranged GPUs that far out-perform competitors in that price bracket.
Cerny and AMD are linked at the hip and PSSR - designed by Cerny, is specifically designed to work on AMD hardware.
Sony could potentially release a portable on par, or surpassing, the power of the PS4pro or XSS. Doing so cuts the legs off of PS5 so they're stuck between a rock and a hard place.
PS5 price should be dropped, as per any normal generation, but doing so now will kill demand for the PS5pro. Not doing so keeps people on the PS4 and, if timed incorrectly, will have the pent up demand of the PS4 players jumping on the switch like hungry fleas on a mangy dog.