Fame

Quoted with approval from the ARG (American Record Guide):

We get a lot of publicity touting the "greatest" — violinist, pianist, whatever. In the age of mass culture "greatest" simply means "most famous", which in turn means "has the biggest publicity budget". And that means he attracts crowds of people who don't know any better, so he plays with every orchestra that can afford him (his fees climb very fast, so many cannot), which feeds his reputation, thus confirming his publicity. Often less famous people play better, but are viewed as "second tier".