> You can implement whatever you want, just not in a website. Write an app instead.
I don't want to write an app for it. By your logic websites should be plain text and we should all be learning N frameworks to do things that are way easier to do in a browser, available without having to install black box crap software on our devices.
It makes no sense, since you can do plenty of worse things than disabling zoom, in fact the browser allows a whole range of things that are not in the interest of users and they don't do anything to curb those, so your point is basically moot.
> In practice, making an inaccessible website is often more profitable because it's less effort.
This has no bearing in real accessibility, it's, as plenty of other things, a red herring, since real accessibility is not defined by zooming or changing your scrollbar appearance - as you can confirm by visiting a very large part of the internet.
> And in many cases, it is better for a website to not exist that for it to be inaccessible:
This is like, your opinion. Which besides being as the saying goes, isn't even backed by any rational argument. Just because you keep saying the same words they don't change reality, unless you're Dumbledore, and you're a character in a book, or a movie, and even then, it only changes the story there, not the story outside of it.
All the cases you mention can, and should be dealt with in legal terms - your school, employer, university, or state, are public entities, there can certainly be accessibility guides, references and standards, as there are in a multitude of others things, exactly to regulate that.
Your argument is like saying, that paper should not be used to draw, or do origami, or write in other languages because someone might not understand what it is, or what is contained in it. Of course, that's silly. And when it comes to government, schools, and public entities, according to the type of documents, printed and available in paper, they do have to follow a specific ruleset, without impacting what paper can be used for in other situations.