That's how ALDI works. They fluctuate with the market prices. But many of the larger chains sell things at a fixed price because that's what lots people want. They will make more money when the market prices are low and less or none when they are high. Many even sell staples like eggs and milk as loss leaders and neve make money off them. Of course things like the avian flu cause exceptions because they're not going to go bankrupt selling you eggs for half what they paid.

People don't like fluctuating food prices.