Because it's blindly following an inadequate heuristic, and not gracefully degrading if it fails - instead, you get comments like these blaming the author. Even though the author never wanted you to use HTTPS in the first place.

> What justification is there for serving HTTPS in a way users can't expect to consume?

Plenty of technical reasons (eg. what the sibling comments mentioned), but most importantly: there's no Internet/Web standard that I'm aware of which would prohibit me from doing so.

For example, you might be running a Tor relay node which would serve the node directory list on :443 to help people bypass firewalls, but also be using it as a useful and legitimate web server in order to prevent organizations from blocking it wholesale.