It must be carried on person (in wallet) at all times ... suppose wallet stolen? A renewal may be denied, so logically if one has a valid Green Card, why would one want to renew it? (Perhaps our age has led to the original photo no longer resembling us.)
Once upon a time Green Cards did not come with any exipiration date. Many now are issued with 10 year expiration. Where are the rules regarding permanent vs. 10 year kind?