HTTP/2 uses a binary encoding instead of text for performance reasons. I prefer the text version myself as it’s easier to write simple tools for (quick clients, telnet based queries, etc).

Is a custom binary format that much more efficient than a gzipped human-readable format? If not, then it makes all sense to have a mostly universal decoder instead of a hundred different ones, especially since decoders of custom binary formats has traditionally been a major source of security vulnerabilities and other bugs even when those decoders have been written by skilled people and used in production for years.

The answer is in your comment. If you add a step of decompression, then text parsing...it's plain-as-day going to be a lot slower then just pushing bits through a binary parser. Less work = faster