So do all file formats.

I don't think you understand what I'm saying.
json, XML files for examples doesn't have schemas by defaults. Schema exists but are totally optional, and are most of the times never there.

The same holds for all file formats: don’t go around licking random bits in a file, use a client instead

Most of the time the file was written by something not implemented to be used by third party.

That’s really besides the point.

As far as I'm aware, I'm the one making the point here.