[bluGill]

Even if you are a prepper, there is always the risk that you aren't able to get home. Maybe you are on a trip across the ocean, maybe you died in the initial attack. As such you should tell your friends who might be able to get to your bunker how to get in without you. Maybe you save a friend even if you can't save yourself.

Also it is easy to have enough food to last for a year or two, but what after that? It is a lot easier to survive if you have a village with you. A village protects against loneliness/depression. A village planting fields makes it more likely not all of them fail (rain/hail is often unevenly distributed even across a small village). A village makes it more likely that useful skills survive - medical doctors (even without modern infrastructure they can still do a lot), various trades can often figure out useful things (if there are enough engineers and some sort of easy power source you might even be able to get an electric grid for your village). With enough people it is more likely someone actually knows enough about gardening to help you grow food.