There is an evolutionary counter-argument here.

Imagine two file formats competing to be "the web":

* In file format A, the syntax is narrowly specified and any irregularity causes it to be not rendered at all.

* In file format B, there are many ways to express the same thing and many syntactic forms are optional and can be omitted while leaving a page that still renders.

Now imagine millions of non-technical users are trying to make websites. They randomly pick A or B. Which ones do you think are more likely to get to a point where they have a page that renders that they can put online? It's B.

Even though the file format of B offends our software engineer sensibilities, in an evolutionary sense it is much more robust and able to thrive because more fallible users are able to successfully write working files using it. It will completely dominate once network effects get involved.