I think WebAssembly is more used than it appears, just difficult to see/tell.
A few years ago I actually tried integrating AR via WebAssembly with Amazon. We couldn't get the approval due to poor performance on Amazon fire devices (which have low end hardware). It is a shame but it is what it is.
What is disappointing/annoying is - as a CTO - it is near impossible to hire someone with WebAssembly skills. It requires an extra curious Engineer with a passion for native and web. Training is always important for a team but when going down the WebAssembly route you need to extra focused and invest more than what a typical Engineer would be allocated (E.g. Increase training from 1 day a week to 2-3). I suppose this may put people off?