Feynman did his Nobel work a long time ago and early in his long career. I suspect that achieving a science-Nobel-level breakthrough these days usually happens many years later in a career, because getting to the outer edge takes many more years of study than it used to. Breakthroughs requiring less study are more likely already to have been made, and each generation has to reach higher for the remaining fruit.

I also suspect that reaching a science-Nobel-worthy breakthrough requires not just more years but more-focused work. Feynman may simply have been an exception, but he might also represent something that was possible then but has become less possible with each passing year.

He is a very rare exception to the pack, I believe. How many biographies have you read that read like "Surely you're Joking, Mr.Feynman"?