This is somewhat stupid from my angle (the W3C recommendation).

I don't expect that url.html is a static html file. I expect it to be server-side generated in 2024. For me site.com/page and site.com/page.html are the same. I do not expect different behavior from my web client side. So I may switch backend engine every year, and I'll just route the request sfrom page.html and that's it.

What's way worse than this is using non-HTML extensions for emitting html. I go to pichost.com/image.jpg and I get a webpage served. This is a bad pattern and it needs to go away. I'm not even going into responding differently depending on user-agent or referrer, if you have combination of these you get JPG returned, if you don't you get a webpage returned.