WebAssembly implies static linking (malloc / printf & all are part of the shipped module) and code size matters since it directly influence users (since there might be delays in downloading big payloads). Both factors plays a role in deciding to plan putting work in optimizations like this.

There are some general gains to be had with this optimization, and probably the same ideas were already around for a while, but putting together in this way was helped by thinking about WebAssembly specific constraints.