What's wrong with <img src="image.png">? Maybe some kind of semantic purpose <img src="image.png" purpose="decoration"> vs <img src="image.png" purpose="graphical-content"> but you can imagine every website owner will think that their logo is graphical content and respectful UA authors will need to disregard the semantic attributes and try to guess based on the presence or absence of some kind of caption, for instance.

UAs could easily lazy load by default on metred connections.

The page layout changes after the image loads, which is annoying as a user. Probably because users have been trained to hate page layout changes that happen a few seconds late because of that dark pattern where you change the page right as the user is about to click to change the thing they click on. How they achieve this on mobile is anyone's guess.