Yes, I find that here too. Our local supermarket, which I walk to, is the "sister" to a larger chain. The smaller one also has more locations. But since it is a smaller store they can't possibly stock the same variety of products that the bigger store does. I can get most of what I want from there but for items they don't carry, I'll have my son stop at the bigger supermarket, which is in the next town (though not too far away), whenever necessary, to pick up what I want. He doesn't have to go that often.
I also shop at Walmart.com which has some very good prices and good store brands of several items. I don't pay for shipping because my son picks it up on the way home from work. I even placed an order on Amazon for a Coffee Mate sugar free, hazelnut creamer because sometimes it's hard to find in the supermarket and the price is more reasonable. Some of their other food items, not so much. About 35% of our food comes from Costco. I would find it hard to limit my shopping to one store, but I love to shop anyway. I have a friend who lives in Florida. From what I hear, Publix is kind of expensive.