If you take off the bark, remove the outer layer, the inedible bit, and roast/toast the inner layer, it can be ground into flour on it's own.
We are "The Cooking Ape". By cooking the bark this way, then grinding it, it makes it much more digestible and nutritious…..and it doesn't screw up the bowels the same way either. It makes flour rather than sawdust if roasted first.
It's basically one of the old 'famine foods'. Not something you'd go out of your way to eat in any quantity unless of necessity.
It's an energy balance thing again though. If it costs more to extract than you gain from ingesting it, it's not worth it.
In Springtime, when the tree is pre-bud break, but obviously warming up to it, then's the time when the inner bark is sweetest. It's also the hardest time of year in some ways. Nothing is plentiful after Winter, and the late Spring/early Summer growth hasn't come on yet. So, the bark was a fill in to the seasonal round.
M