Not everyone has a fridge and/or freezer, so not everyone is able to buy and store a couple of weeks' worth of fresh/frozen food.
Some people only buy a few days groceries at a time because they can't physically carry two weeks' worth of supplies but don't have a car and can't afford taxis.
Some people struggle to get by pay cheque to pay cheque in a low-paid job or payday for meagre benefits. Some are reliant on foodbanks to feed their family. Not everyone can afford to stockpile.
Not everyone is in a position to stock up and make sure that they have sufficient provisions for themselves and their family for a couple of weeks, because they lack the finances or storage capacity or because of logistical problems and they lack the means to transport a big shop.
If you're able to, bully for you, but you might want to check your privilege and have some sympathy for those who are less fortunate, who are struggling to get by.