There are several reasons for this:
1. Gigantomania – I'm not sure if this is the correct term for this type of purchasing preference among shoppers. People buy with their eyes. Looking at a store shelf, they choose a product that appears to contain more, based on their visual assessment. For example, when looking at other products in a 1-liter package, they will likely choose these products over a highly concentrated product in a tiny bottle, even though it's clearly labeled a concentrate.
2. Purchasing habits – for years, people have been buying this product in larger packaging (for example, a 1-liter bottle). If a manufacturer intends to switch to concentrates, they must consider that potential buyers will perceive the product as a reduced quantity at the same price. They will feel cheated and may abandon the brand altogether. It's too much of a risk for the manufacturer.
3. Safety - A highly concentrated product can be very dangerous. For example, it can be highly corrosive and pose a risk of burns. However, the same product heavily diluted with water poses no such hazard.