The reasons to use HTTPS on a blog or everywhere regardless of whether there is data that needs to be secured are mainly to fight against things like censorship or ISP surveillance.
If you really don't think your website is going to be censored, that leaves the problem of ISPs injecting content. Maybe he doesn't feel that is a big problem, or that there is another way to fight it.
The big push for everything to be https is about making it hard for governments or ISPs to say that some site or another should be an exception.
It's kind of like, wearing masks.. before the policy was that everyone should wear a mask, best to keep it simple and not try to make exceptions that way we will get the most adoption.. except for sites like this, it's like you never actually talk, and have been vaccinated so you are not worried about catching anything and don't wear a mask.
The other part of this is that for people like me who have been serving http for so many years, the campaign for https just doesn't hit as hard as for young people who really grew up with that mindset being preached to them constantly.
But in the end, I think that it is better if everyone does it. Just maybe not quite as severe a problem as you think if a few people slip through the cracks.