Because /etc/letsencrypt is listed in the package contents, you can't install certbot when the files already exist, such as when you're using files you backed up earlier. You get an error "failed to commit transaction (conflicting files)". It should be possible to back up /etc/letsencrypt, copy it to a new computer, then install certbot and have it use those files. There's no good reason for it to fail installation just because files exist. certbot is perfectly capable of using an existing /etc/letsencrypt directory.