Wouldn't it be more accurate to say that WASM hasn't passed the PoC stage? There are quite a few languages that have great WASM support, to the extent WASM allows, but have to bring all kids of workarounds to deal with the shortcomings of WASM as it sits. An especially challenging problem as it relates to browser use with those workarounds is that they bloat the artifact size. Few are willing to subject users to multi-megabyte downloads.

Work is being done on WASM to address those shortcomings, but hands are pretty much tied until that arrives. Until then, the "lower level" and heavily constrained languages will be left to stand alone.