Leica M vs Leica R

I never understood why I can buy a used Summicron R 50/2 for 150€ and a used Summicron M 50/2 will cost me 1000€+

Is the R lenses so much worse in image quality? Is it just the myth and allure of M bodies? Basically I want to know if it’s a factual difference in quality or just more demand and M-myth that makes the Ms more expensive?