I disagree that (most) files contain their own schema though. Sometimes the schema is incorporated by reference in the metadata, sometimes in the key name (filename).
Some structured data formats contain a sort of self descriptive sub schema, but they always(?) require something higher up the chain to make sense of it. I can't think of any examples where that isn't the case, but I'll leave the question mark on the always because I'd like to be be proven wrong!
When you reach many, many files, just try to get people to tag them. Just try.
How do you tag a file when you can't find it to tag it, and when do you tag a file that you've forgotten about?
Ultimately, someone comes up with yet another abstraction that makes it just a little bit easier... Now, if we made every application those wrote a file also tag it meaningfully, and then had meaningful translations, and.. oh geez. I normally just delete everything and start over when I realize I have no idea what 90% of the files I just scanned were for. If they were truly important, I would've known what they were. I guess the people with ten bazillion files on a PC are just data hoarders. "But, but, but I'm going to need that report one day!" (Bet you would tag it, now wouldn't you?)
First link for "digital hoarding", but there is more to read about it.
Files do exist. They are the values in the filesystem KV store, but they are also a schema for the value so that interoperability works. If we followed your logic, apps would not exist either but we all agree they do.