The author is likely not updating it anymore, so you are effectively complaining to a group of people here that can do absolutely nothing about it.
However, that has been discussed on many other topics that are directly to do with TLS/certificates etc. so I don't think it's worth bringing up (aimed at the OP) every time there's an HTTP linked.
Maybe rewritten it could be viewed as a warning for those who care instead of a criticism.
Whether or not that matters when viewing this particular site is up for debate
If that's a big threat vector, I feel like the much bigger risk would be visiting malicious sites, not a local or ISP located attacker injecting stuff into benevolent-but-HTTP-only ones.
Another trick that could easily be pulled by a malicious ISP/wifi provider is to insert a redirect into the HTTP page to go to an HTTPS site controlled by the attacker (presumably with some semi-related name so as to not seem suspicious to the user) and to then bypass non-HTTPS restrictions in the browser.