Exactly. When I'm using an application called a browser to view a document on the web, I don't want the document to try to become part of the chrome: that break

Exactly. When I'm using an application called a browser to view a document on the web, I don't want the document to try to become part of the chrome: that breaks the "web page" metaphor. There is a very small subset of websites, such as Figma, that feel more like independent applications than web pages, and for those I get more annoyed by the presence of the browser chrome, for basically the same reason. What's worse, almost no sticky header has any useful items in it. Take StackOverflow as an example. It has a link to the homepage and a searchbar, in spite of the fact that many frequent StackOverflow users have never visited the homepage and never used the built-in search. The top of the screen is the most valuable part, because my head is usually above the screen, so it's more comfortable for my eyes to rest around the top of the viewport. So if you put something there, it had better be important.