The JSON Schema spec was abandoned by its original authors, and was picked up by a series of other people with varying levels of standards experience (myself included).

Personally, I had some promising support from my then-employer (including an IETF connection), but then it kind of petered out, and I was buried under other stuff and had to pass it on. The team who picked it up since them seem pretty on-the-ball as far as I can see, so I would still recommend it as a useful project to contribute to.

It is supported by some tools - last I heard, Visual Studio could use JSON Schema for autocomplete and validation, as well as a couple of databases. I used to get a few million NPM downloads a month on my validator, so someone's clearly using it.

Unfortunately, power complexes. When more power is needed than json has (e.g. a schema language), there is xml and the xml ecosystem (e.g. xs), with all the tools, features and standards you could possibly want... actually, more. Thus, it is the complexity of xml that keeps json simple.

It is the same principle as keeping flies off the dinner table by dumping a pile of manure outside the front door.

No we don't. Typescript is _great_ for this.

  type Book = {
    title: string;
    author: Author;
    isbn?: string;
  }

  //etc

It's easier to read and write by humans than JSON-Schema, a large amount of programmers are already familiar with the syntax, and it's pretty self-explanatory to most programmers who are not.

Sure, it doesn't have constraints like "maximum string length" and "must start with a capital" etc, but I'd wager that those don't really belong in a schema language anyway. The structure and the types is what matters. Once you got that covered, doing some validation on the content of the values is easy. And you can use a Real Programming Language for it, instead of something half assed.