That is correct, in theory, but there is a large gap between theory and practice. How practical would it be for, say Three.JS to generate shader bytecode? Would it need to depend on a sophisticated WASM module that allows to build such bytecode? Who is going to build that?

Google has spent a lot of effort trying to answer these questions, and they got close, but in the end the text-based solution prevailed. In part, because it was easy to agree on for all parties.