One advantage of the prolific Japanese convenience store (or "konbini") is that any improvement in the underlying franchise system can be rapidly deployed to all franchisees (like nodes in a network). This is true of many franchises, but the konbini are exceptionally prolific, so this effect is magnified.

For example, if there is an opportunity to increase efficiency, or reduce costs or environmental impact, it would be relatively easy to deploy this throughout an entire franchise, as compared with heterogenous stores.

As for the issue of opening hours, labour shortages and demographic trends (the population is aging and decreasing) are significant. I am only aware of two likely solutions which are not mutually exclusive: (1) immigration; and (2) automation, ie. robots. Increasing the fertility rate might also address this issue, but seems less likely to happen.