1 week of supplies is more about flexibility. In survival situations once things get bad they snowball. People aren’t going do drop dead on day 8, but think of it as having a week to prepare for a known disaster before you need to worry about the basic necessities. 6 months is hypothetically better but far more expensive and it would only make an actual difference in a tiny number of situations.

Further it’s fairly trivial to cycle through a week of supplies and keep it fresh. Looking at the shelf life of what you regularly consume, find stuff that lasts a while, get a little extra, and then keep restocking as you normally would after that point. Just remember first in first out.

PS: It’s honestly surprising how long some stuff lasts, honey in an unopened glass container is going to be good long after you’ve died of old age.