Part of the business model is to work with manufacturers to offer smaller packaging, i.e. less product, for the same price. Consumers are more sensitive to price and not unit price.

Another strategy would be "shrinkflation" (great Planet Money coverage on this: https://www.npr.org/sections/money/2021/07/06/1012409112/bew...). Over time you'd just sell less stuff for the same price point.

But yes, some of the various Dollar stores have left the strict $1 product rule.