The R&A can stick with a rota of old courses because - as far as I know - there are no modern courses in the UK that deserve to crack the rota.
That's not the case in the US. Rankings aside ("tradition" weightings assure that old courses will dominate rankings for the rest of our lives), there are lots of modern courses in the US that deserve to be on both the USGA and PGA rota.
Some of those moderns have been noted above. I would add Cuscowilla which, unlike many other moderns, is about 1 hour from a major airport and has the infrastructure to support transportation, parking, hotels, etc. for 30K plus attendees every day.
The bottom line is that the rota of older courses used in the UK is not a model that applies in the US. There have been too many great courses built in the US since, say, 1970 for that to be the case.
Bob