The original google proposal was to simply use SPIRV. A compromise was then settled for the intermediary language to be isomorphic to SPIRV, removing some of the warts and edges of it and make verification easier.

However, Apple with the help of the Mozilla folk successfully managed to twist the semantics into something that is no longer easy to translate from and to.

Game developers don't want to work with WSGL, the whole point of the new WASM and WASI ecosystem is to allow devs to bring their own tools.

This is especially bad for something like a shader language, where you want to squeeze every bit of performance out of the hardware, often with hand rolled instructions. Having the browser run a mangled version of the SPIRV that you or your toolchain/engine e.t.c. produced is simply not acceptable.