Why don't more people grow their own damn food?

I see stories of so many people struggling on food stamps in the us and over here, not getting enough money even if they're working or if they're on benefits to buy enough food. I've been gardening for a while and can't believe how ******* easy it is to grow food. seeds can cost pennies and you can buy large amounts of potting compost from places like b&q for so little. if you don't have the land (and a lot of people do have access to some land - even the people who are struggling), you can just grow randomly aka guerrilla growing, so there's no excuse. So why are more people not growing their own food? It doesn't have to be expensive or hard. I just don't understand why it's not more popular, even if it doesn't give you short term results.