"If you try to do that in pop music - to play only rare show tunes, for example - people don't come"

This quote by Bobby Short is referring to the difficulty of playing uncommon program tunes in pop music. He is recommending that if an artist tries to play just rare show tunes, people will not pertain to their shows. This suggests that the audience is not interested in hearing uncommon program tunes, and instead prefers to hear more popular music. This could be because they are more knowledgeable about the pop music, or because they are most likely to dance to them. It could also be because they are more likely to sing along to the popular songs. Bobby Short is recommending that if an artist wants to draw an audience, they must focus on playing popular music. This is since individuals are most likely to come to a program if they know the songs and can enjoy them.