For a good discussion into why _all_ websites should use HTTPS, and the many different ways that not having the connection secured is actively harmful and why should not be done in the modern era.
https://www.troyhunt.com/heres-why-your-static-website-needs...
Not having your site as HTTPS puts all of your website visitors at risk. Even US ISPs like that of Comcast use these very same practices to inject warnings into insecure web traffic[0], some of which look more like advertisements than warnings. And like mentioned in the article, promises from ISPs not to use it for advertisements are just that, promises, and those can be broken in an instant. And when you have the power to inject anything without notice, you can do anything and everything with the website experience. You can attempt to force a download, present scam pages that look like antivirus warnings or software updates, one of the easiest ways to have users fall for malware.
We should _never_ expect regular non-technical users to have all of their threat models in mind, nor should they be expected to understand all of these differences. Website owners should be expected to protect all of their visitors as best as possible and one of the easiest ways to start is by protecting their website with modern HTTPS encryption. Otherwise, it would be like a chef leaving the bones in a salmon before serving to a customer. You could do leave them in, but a customer might not know they are there and you have left a choking hazard.
[0]: https://gizmodo.com/comcast-to-customer-who-noticed-it-secre...