Because there is a fundamental difference between file contents and
filenames. Filenames are supposed to be text.
I think this is actually the fundamental point where we disagree.
You think of filenames as something the user types in, and that is "readable text". And I don't.
I think the filenames are just ways for a _program_ to look up stuff, and
the human readability is a secondary thing (it's "polite", but not a
fundamental part of their meaning).
So the same way I think text is good in config files and I dislike binary
blobs (hey, look at /proc), I think readable filenames are good. But that
doesn't mean that they have to be readable. I can well imagine encoding
meta-data in the filename for some database that uses the filesystem as
its backing store and generates files for large blobs. And then there
would be little if any "goodness" to keeping the filenames readable.