For the same reason any of them are adjustable? Different usage scenarios, different types of contents?

Because you might have to adjust it as the weather/climate around you force you to adapt to it. What temperatures you run in the summer might not work in winter (especially in countries where you get -20C sometimes, and summers are ~25C), and autumn/spring might need adjustments by the day, especially as we start getting more extreme shifts nowadays compared to just some years ago. Heavily depend on the individual store, some are very barebones.