I have knitting needles that belonged to both my grandmothers plus some that belonged to DH1's great aunt. Likewise crochet hooks. My eldest daughter has made up her set of crochet hooks from my collection, so that's at least four generations. It wouldn't surprise me at all if some of the needles and hooks belonged to my great-grandmothers. One or two of them appear to be made of bone. Fairly sustainable, or rather, sustained, I'd say. 
The cynic in me says Don't kid yourself — bamboo knitting needles are made for profit! Funny how they started appearing when knitting got 'fashionable' again in recent years. After all, most, if not all, metal is recyclable and, as several of us have shown, metal knitting needles and hooks last a very long time if looked after.