That doesn't mean it's always easy to install and manage keys. For example, the author of the passh tool recommended by this post somehow managed to come away with the impression that OpenWRT's ssh server only supports password authentication.
Another example: Ubiquiti gateway consoles like the UDM-Pro. You can install an SSH key but these are erased on reboot. So after every reboot I have a script that uses the SSH user password to re-install an SSH key but this can’t be relied upon and I haven’t found a way to make an SSH key persist.