Well..except they do? HTTP is an anomaly in having largely human readable syntax, and even then we use compression with it all the time which translates it to a rarefied symbolic representation.

The limit beyond that would be skipping the compression step: the ideal protocol would be incompressible because it's already the most succinct representation of the state being transferred.

We're definitely capable of getting some of the way there by human design though: i.e. I didn't start this post by saying "86 words are coming".