Innate musical talent is undeniably a prerequisite for greatness. It's a requirement but one of many. Let's say that in any group of 10,000 people in the world, there is one person with the innate ability of Bach. (The plethora of painting geniuses in Renaissance Florence shows that this number is unlikely to be much bigger.) The likelihood of Bach is less than one in 1 billion (to restrict ourselves to 1000 years of Western music and assuming that Bach is the greatest and that the total population over 1000 years of Western history is over one billion, which must be the case), not one in 10,000. So assuming all these variables are independent (a big if, I know), we need to explain the remaining 1/100,000 likelihood. I think the rest is culture and character.If talent is evenly distributed by genetics (not sure it is, but just for the sake of argument), then why doesn't every city have the artistic flourishing of Athens in the 5th and 4th centuries BC? Names to note: Socrates, Plato, Aristotle, Thucydides, Sophocles, Aeschylus, Euripedes. Or of 15th century Florence? Names: Michelangelo, Leonardo da Vinci, Botticelli, Machiavelli, Brunelleschi (who designed the Duomo). Or 16th century London? Names: John Dowland, William Shakespeare, Sir Francis Drake, Christopher Marlowe, William Byrd and Thomas Morley. And of course, 18th century Germany and Austria. This flourishing was less concentrated with Bach in Leipzig and Haydn, Mozart and Beethoven in Vienna.
There are brief periods of intense flourishing surrounded by dull stretches of mediocrity. Some factors are undoubtedly historic. Wars, revolutions and social unrest undoubtedly drain resources and redirect talent away from the arts and humanities. But the role of culture and character also seems to be important. Some cultures seem to produce more art than others. Some kinds of character seem to produce more arts than others. The role of patronage also seems crucial. The society must be prosperous enough to support artists and must value the arts highly enough to support them. In Athens the whole population went to see the plays just as in Leipzig, the whole congregation heard Bach's cantatas. My commentator's assertion that a faculty of hard work and an intense curiosity both played a role is also correct.
I also think that artists compete with one another and learn from one another, which is why we get communities of artists that because of mutual influence produce more interesting work than they would have if they worked in isolation.
Well, this could go on and on, but I'll close here with this: