I used to work in POS and you'd be surprised at how difficult it is to produce uniform POS software. It seems like all retailers have slightly different ways they want things done and were willing to pay, what to me is, a surprisingly large amount of money for their differentiations.

It's extremely common for these companies to consider their POS/supply chain software is a core competency. So Major Dollar Store A would want to make absolutely sure that none of their code changes would be made available to Major Dollar Store 1, even if it were mundane stuff like tax code changes.

On one hand, it's good money, because it is such an integral part of their business. On the other hand, it can be tedious to redo the same thing after the sales staff sells the same customizations with minor differences.

Most point of sale software is incredibly fragmented down to hyperspecific use cases. A former company I worked with was partnered with a POS software that was made to service plane re-fueling stations for regional airports if that gives you an idea how segmented that market is.

what @jsonne said. They had specific controls built in for inventory management, automatic re-stocking, etc. Also I think it had to accept EBT payments for certain food items as well.