The problem with that is, if everything is highlighted, nothing stands out.

Broken syntax should not be highlighted too. So Tonsky recommends to

Highlight names and constants. Grey out punctuation. Don’t highlight language keywords.

and because developers are not payed to the line of code anymore, "Comments should be highlighted, not hidden away."

Many developers prefer the dark mode because the dark mode can have less vibrant colors.

I suspect that the only reason we don’t see more restrained color themes is that people never really thought about it.