I think they do this to make it harder for an exploit to just run the command to get the keys. I'm torn whether I think this is really an issue or not though. From a security standpoint it is one less attack vector to get my 2nd factor keys. From a usability standpoint it is annoying when I switch devices. I personally solved this problem by storing my two factor auths on my yubikey neo which is a bit more portable. I don't think there is a way to get the keys off of there either but at least the key itself is portable and works with Android and all my desktops/laptops. I am not sure if they ever figured out iPhones though.