I think the motivation for using HTTPS with static content is to prevent man-in-the-middle attacks that inject advertising or malware into pages. I have read about governments, ISPs and hotels doing that sort of thing.
One example of what can be done is to cause the users to DDoS a third party.
The man-in-the-middle attack potential other replies have mentioned is possible, but my reason is far simpler. Defaulting to https for everything removes the cognitive load of having to decide whether to trust a website and pushes users to believe everything should be secure by default. The environmental impact is, in my opinion, worth it.
http is still susceptible to man in the middle attacks even if the site contains no secrets. You have no guarantee that the contents of the website haven't been tampered with (not that attackers would have much incentive to tamper with a blog).
That's pretty much my point, there is no reason to meddle with the contents here. It's different if you live in a country where your ISP automatically MiTMs you (as a sibling comment to yours pointed out), but that's not a thing here at least. If you know that's a threat and it bothers you, you would likely already have measures in place anyway?
