Why are so many internet protocols text-based?

Textual data and exchanges are often self-describing. They're easier to debug and monitor visually. Try debugging or reverse-engineering binary exchange with some obscure proprietary protocol to see why this matters.

In the end it is more about human convenience on the highest levels of OSI and less about transfer efficiency.

No one there mentioned the Unix Philosophy.

"Text is the universal interface."

en.wikipedia.org/wiki/Unix_philosophy#Doug_McIlroy_on_Unix_programming