64 bit addressed cannot come soon enough. In certain domains the entire data set you want to work with is many times the 4GB limit, and JS has no such restriction so it’s a PITA that WASM does.
It's because deployment is a harder problem than development (at least, it's harder for developers, because deployment is a social problem). The web is a pretty poor development target (though it keeps getting better), but it's a damn terrific deployment medium, and that's a winning tradeoff.
I'm still seeing laptops sold with 4GB which would be used really quickly.
(Also these apps are not necessarily written in JS, it's a compile target too)