Good question. Two different type of buyers/collectors. The majority of the people buying/building these high quality RSR builds are most likely the same people that can afford a collector grade 1976 Turbo and probably have one in their collection.
Here's a guy building 3 of them at the same time on RL.
https://rennlist.com/forums/911-forum/973916-my-rsr-build.html
This was a real nice build that fetched all the money. Well marketed and good timing.
https://bringatrailer.com/listing/1984-porsche-9111973-rsr-recreation/