Bamboo is not wood, it is an extremely fast-growing grass. So there's no need to nourish a complete ecosystem for a decade or two — so the trees can grow to a proper size — and then clear cut the area, leaving animals homeless, and without their usual territory.
The plants can also grow in much, much higher density than trees…because they're not trees, they're grass. So they'll grow together to create an almost impenetrable screen if you don't thin the plants out while they're young.
There are also fewer pests for bamboo, so pesticide costs are far lower, and they don't require a lot of care, pruning, etc. Bamboo is very much a “set it, and forget it” kind of plant. It's also easily crafted into furniture, arbors, fences, decorative pieces/art, etc., and is incredibly durable without requiring a lot of preparation, or chemical stains/fixatives.
So…grows fast, easy to harvest, easy to craft, and doesn't need a ton of chemicals, that's what makes it eco-friendly.