No one is selling exactly the same goods anyway, not at that level.
All purchases (wholesale, retail, whatever) are actually auctions, and they remain auctions even if you aren't aware that they are. So if someone was saying to themselves "Dammit, Kroger sells lettuce so high, I could that I could sell it for 4% over cost and still be 20¢ cheaper!" then they are deluding themselves. Ignore the overhead of opening a nationwide chain and all that other stuff.
When they go to purchase lettuce wholesale, as a new competitor, more lettuce doesn't pop up in the fields instantly. Or even quickly. So you end up causing wholesale prices to rise, at least until the agricultural sector catches up, if it does. They were always careful to grow just enough that none of it ends up unsold. Even if you could source it, likely you're getting the lower quality lots (the stuff Walmart goes after just so they can have theirs priced a penny cheaper, that turns slimy 24 hours after putting it in your fridge).
This discourages new entrants, competitors. And gives Kroger some slack if someone does decide to try it.
> They were always careful to grow just enough that none of it ends up unsold.
It is a market. However much they grow, exactly that much will end up sold. They'll drop the price if there is unsold inventory to sell it.
They can't be doing a physical estimate of how much lettuce people eat. If there was any variance at all in how much lettuce gets eaten (which there is) then there'd be constant lettuce shortages where the shelves were empty. That doesn't happen, so we can tell that they are using price signals to control how much gets sold.
All purchases (wholesale, retail, whatever) are actually auctions, and they remain auctions even if you aren't aware that they are. So if someone was saying to themselves "Dammit, Kroger sells lettuce so high, I could that I could sell it for 4% over cost and still be 20¢ cheaper!" then they are deluding themselves. Ignore the overhead of opening a nationwide chain and all that other stuff.
When they go to purchase lettuce wholesale, as a new competitor, more lettuce doesn't pop up in the fields instantly. Or even quickly. So you end up causing wholesale prices to rise, at least until the agricultural sector catches up, if it does. They were always careful to grow just enough that none of it ends up unsold. Even if you could source it, likely you're getting the lower quality lots (the stuff Walmart goes after just so they can have theirs priced a penny cheaper, that turns slimy 24 hours after putting it in your fridge).
This discourages new entrants, competitors. And gives Kroger some slack if someone does decide to try it.