It's not really an "excuse"; a normal CA is not — cannot — going to sign a certificate for "localhost"; it wouldn't make any sense, and the verification methods that prevent any random joe from getting a cert for "google.com" wouldn't even work against localhost, or when you're pretending to be a domain you aren't (obviously!). (E.g., "example.com" in the article.)

The only way to use a real CA such as Let's Encrypt here would be to actually have a domain name. While I do have my own, I'm not going to us that at work. While my work has a domain, of course, we manage it with Route53, and AWS doesn't support delegating control over a subtree in DNS via IAM — that is, it's not possible to restrict permissions on a domain s.t. I could have a subtree to myself. (I've complained/feature requested this to AWS, but their responses have been less than enthusiastic.) Aside from not having a domain, I don't have an IP at work, as we're on an IPv4-only network and connection.

While none of this makes it impossible to use LE, it requires effort from people that aren't me. Tools like the one in the link fill a real need.