Because artists can be extremely eccentric and insane, and unfortunately, the people they hurt the most are the people that are closest to them.
He's a world-famous name to people who care about his music, but there are many people who have never heard of George Gershwin and those numbers increase.
People realize that Salieri is not the man we saw in the Amadeus movie. That man had no talent. It was a great movie, but the Salieri character was a big fiction.