I'm not even entirely sure that the act of consuming it yields more calories from consumption than consumed in exertion for humans.
Most species that subsist on bamboo are sedentary and spend significant fractions of their time and energy simply masticating.
There's more than enough calories to sustain life in a Thai green curry with bamboo in it ;-)
This resilience applies to the part below ground too, and they're full of water, so it's a bit like trying to dig watermelons out of the ground, but if inevitably split one while digging, and you miss a bit it's just going to grow again, and if you take too long between bouts vs the plant (as with bamboo it's unlikely to be a 1-day affair for a reasonable size clump), some of the bits you cut will have broken down and started to rot, so the ground will be soggy and smell horrible.
Can you summarize what you've learned?