Here is a wild guess: a new kind of store sells only the top, say, 50% of items in terms of sales numbers, and sells them for a little less. People out shopping for things all from that group go there. But everybody needs the bottom 50% sometimes, and when they do, that store is no longer around.
This was a better argument before the internet. Nowadays I don't think it's worth paying a 30% markup on everything so that one thing you sometimes want is always within driving distance.
At the end of the day people shop where it's convenient and cheap, with a bit of a tradeoff between those too. Some people like spending more at a locally owned place, but most would rather pocket that extra cash.
