People, for reasons we don't know, understand or maybe without reason at all, put their professional reputations on the line all the time. Most of the time it goes by unnoticed.
WASM just skips the JS to JIT compiled bytecode - correct me if I’m wrong. Creating a standardized bytecode for distribution that other languages can compile to.
No reason to continue to shackle the web to JavaScript.
https://hacks.mozilla.org/2018/10/webassemblys-post-mvp-futu...
Another reason is JS already has many high level features. Which might make it easier to implement similar ones in your language if you target JS directly.
The last reason I can think of is interop with existing JS code and the DOM.
Better WASM/JS interop is on the way, though atleast on Firefox nightly you can get this for fairly low cost for some functions.
GC is also on the todo list and IIRC might get an early preview in Firefox Nightly.
Once the GC is done, DOM integration will happen, people are eager for that and that would eliminate a lot of the necessary JS glue code.
So the only thing people want to do with WASM is deploy C/C++ to the browser and for raw speed?
There's many other reasons you would want to use WASM...you might want to use languages with better tooling or better suited to the purpose of your code (I'd rather do UIs in Lua than JS 10 times out of 10). Maybe you want a tiny memory footprint so you can run on small devices. The list goes on.