It is absolutely not a security feature. It’s a feature so a site can serve static file without risking them being hot-linked as resources to be used in a website. For example, you can’t hotlink github’s raw content from repositories as a style or script src on your website. It has nothing to do with a site’s security. It’s all about a site being able to offer a service without having their service abused by users.
If you are worried about other places using your server’s resources as content for themselves, there are already ways of handling that in your web server config. Checking the origin of the request and denying it if you don’t recognize it. There is absolutely no need for a new strict mode to have anything to do with hotlink prevention.
It’s not as easy as just saying they’ll know, and boom they’ll know. In reality, most users have no idea what’s going on so they blame the closest thing to them, the browser. Because that’s what they understand to some degree.