For some it is a traditional way of life. Some understand the insecurities of life. They realize either through experience or through listening to others. How fragile any supply system is.
The smallest of events can effectively empty all the shelves in the stores on your area.
With many only buying what they need for one meal at a time failing to have at least some supplies could and will cause mass hunger or even possibly starvation.
Yet the media calls everyone who believes in following the old traditions of having a stocked pantry hoarders and makes them out to be criminals of the worst kind.