Just because the forest has more
mass does not mean it produces more
food. Trees produce tons of mass in an evolutionary war to be taller than all the other trees and get more sunlight. None of it is edible though.
All of them are in a highly competitive war for resources. Plants produced poisons to kill other plants. They try to spread their seeds faster. They try to grow taller and faster and steal sunlight. They grow bigger roots to steal water.
No plant wants to be eaten, and so many produce poisons and thorns other deterrents. Few of them keep all their calories in one place, and require highly specialized digestive systems which humans don't have.
The exception is fruit plants of course, but they only produce the minimal amount of food necessary. The fruit you buy in a store has been extensively bred by humans to be so large - and this domestication has a massive energy cost that makes them uncompetitive in the wild.
Anyway the point is that the wild is not optimized for humans at all. It's an incredibly inefficient way to produce food. The plants are spending most of their resources fighting each other, and insects, and everything else. The winner of this game is whatever plants reproduce the most, not the ones humans want. Permaculture is really cool, but you are never going to get anywhere near as many calories per unit of land.