The Top 40

I believe it is a combination of three things

1) We've reached the near limits of what we can with current technology and scientific understanding

2) We're killing off 4000 of our own babies a day and among them are almost certainly these sorts of people

3) Culturally and legally, innovation, questioning stated authority, risk taking, and ambition are suppressed and even attacked.

Only in a free society can one find an Einstein or a Bohr. In a suppressed culture, you will get a Lysenko.

An inquiring mind cannot be quelled.
There is innovative success today but the toilers are not quick to broadcast it for they will be chastised. So we reach for our goals long into the night because we must.

Among other things, I am developing a means of getting 8X the horsepower out of solar cells for 2X the cost. I'm doing it for me.

Oh, there are still great things going on in mathematics and physics, but the dominant people aren't as well known and, because there are more of them, they aren't as prominent. Look at the 1927 Solvay Conference, 29 physicists in the photo and almost all of them famous. These days a similar conference might have ten times as many.

That said, I do think incentives/environment count. Five famous Jewish mathematicians and physicists came out of Budapest over a period of some 15 years. ISTR that part of the explanation was that a dentist ran a science discussion/education group in the city. Athens had a similar bloom for literature and philosophy in its golden age. And sometimes the age just seems propitious.

We're still trying to understand the pre-Cambrian 'sudden' multiplicity of forms of life.
If we now had another Einstein, or brilliant quantum physicists, we might have to deal not with consequences of E= (m)(c squared) but with the the new equivalence of --- "Any remark by President Obama = Idol Chatter."
When we ignore the deadly dummies who rule, why bother with another Einstein.