Just a wild guess but: code is done by developers, and most developers like good code, hence the use of linters.
HTML on the other hand, is arguably not "code", it's markup. And it's also written by non developers on many occasions, and those "non developers" might not want to lint it (if they even know what a linter is).
Indeed, HTML is not a programming language but it's still one of the three pillars for making a webpage. But since we strive for the best code quality, why shouldn't we do the same for markup?
Quality standards should indeed be the same for code and for markup (and also for anything we type, actually).
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