Just look at the official HTML and JavaSc.. nay, ECMAScript specification docs[0][1]. You'd sooner end up with a headache than a functional website if you had no other choice but to use those ;)
Additionally, most initiatives aimed at improving the situation have only resulted in yet more overhead in the form of additional committees with each their own agendas and procedures, or the creation of another new deeply interconnected but otherwise completely separate sibling standard[0][1][3][4], fragmenting things even further.
I used to be quite heavily involved with some of the more meritful of those initiatives, but at some point realised that despite all the time and effort I was putting in, nothing really meaningful/impactful had been achieved or was even anywhere in sight, and it was also becoming too costly on a personal level. Guess that's my justification for having the right to post this rant :)
[0] https://infra.spec.whatwg.org/
[1] https://webidl.spec.whatwg.org/
CSS specs are likewise very readable and extremely useful reference, though they’re less precise than significant parts of the HTML Standard. But if you have questions about how certain things fit together, or corner cases in certain properties, MDN is normally useless while the relevant specs are regularly invaluable. I highly recommend being familiar with reading these specs if you’re doing even mildly unconventional things.
The ECMAScript Language Specification: it’s not like either of the other two; it’s not a document that describes how things are supposed to act or how to use things, but is full code for implementing an ECMAScript engine—just expressed in natural language rather than a more accustomed programming language. I’ve referred to it a number of times when I’ve had nuanced questions about exactly what the engine does in such-and-such a case (the sort that the vast majority of web developers will never need or want to ask), and it’s been useful in such cases once it finally loaded, but it’s very firmly designed for implementers, not users. Covering any of the sort of stuff that MDN covers in documentation was never anywhere near the intended scope of the ECMAScript Language Specification, nor should it have been.
The specs and MDN serve quite different purposes, and something that combined both functions would be poor at both functions. Bemoan not the necessity of either: rejoice rather that you have both!