Sure, it's the dev's website. But the browser is my user agent, not your developer agent. It is fundamental to the purpose of a web browser that it should prioritize the wishes of the end user over those of the server.
This is exactly what's going to happen. If the site's owner for some reason looked for my business — well, the developer's priorities were different, tough luck!
Ooh, that's a bit much. The website dev is pushing their side.
No user of the site is forcing anything onto any other user of the site.
Perhaps we can have an HTTP header or something that says to the site, please don't mess with browser behaviour. Omit that and the site has got implicit permission.
The website dev is generally the one paying for and providing the website... Why is it you expect the provider to bend to the whims of the user? The user doesn't need to use the website.
That's like saying Crest should make orange toothpaste because you don't like the color. Don't buy their non-orange toothpaste.