Why is there so rarely anyone in the shops in RDR1?

I'm so annoyed that I constantly can't buy anything in the shops. General stores, gunsmiths, doctors. They're shown on the main map, but when I travel there, there's usually no symbol on the minimap and no one behind the counter. Saving and going back later often doesn't help either. It's completely random when I can visit a shop and when I can't. Is this just happening to me?