Where I live mushrooms are by far the most abundant wild food. It's good exercise, very enjoyable "work", and they taste really really good with a huge variety of flavors.

Leafy greens also have very low calories per pound. We eat them for the nutrients not for the calories. Because of mushrooms and wild greens, I buy very little vegetables, all I need is relatively cheap (per calorie) foods to go with the wild stuff.

There is also risk of food poisoning with food from restaurants or the store.. not to mention the chronic poisoning of eating food grown with excessive pesticides etc.

For the most part the abundant edible mushrooms look very different from the dangerous ones. But yes you do need to know ID thoroughly if you go for certain species.

That said not everyone lives where edible mushrooms are abundant, I'm not trying to suggest everyone should do it.