Minecraft wiki entry for Best_biomes_for_homes, associated text: Lots of wood: a single tree can yield between half a stack and over a stack of dark oak wood.
Huge mushrooms naturally spawn among the trees, giving the player a renewable food source.
The canopy of the forest is safe as mobs do not spawn on the leaf blocks. The player can navigate and travel over the forest quickly as there are little to no obstructions.
Woodland mansions can spawn here, which can provide shelter and valuable loot from the mobs inside. The mansion can be turned into a base once cleared and looted and is generally easy to find after doing so because of how large and easy to notice a mansion is from far away.