You're obviously correct about what most people do, but most people are also pretty unhealthy and the point of advice is that people have room for improvement, so it's not really relevant what they currently do.

Undisciplined

If you value having redundancy enough, then yes, being self sufficient can be worthwhile. Most people would probably just forgo the tomato or substitute it until the market has resupplied. Likewise for valuing nutrition. It can make self sufficiency worthwhile, but most will seek nutrition from supplements rather than backyard gardens.

nullcount

We should all try and be more self sufficient and eco friendly.

Billy_Dow

That's not at all the point. If I have a tomato plant on my deck and the store is out of tomatoes, then I still get to have some tomatoes on my sandwich. 

Also, see the point about commercial vs garden produce traits. An activity can have very poor returns to scale without being unprofitable.