Why do solid bars last so much longer than liquids? I read an article that explained liquid products often have a lot of water added. Solid bars are more concentrated, so you use less each time. That directly cuts down how often you need to buy more. Less buying means less packaging and less waste overall. It's a straightforward way to save money and reduce trash.
Solid bars can actually wear down faster depending on how you use them. A bar of soap left in a wet dish gets soft and melts away quicker than a pump of dish liquid. The packaging savings are real, but the actual product life isn't always longer.