Right which is part of why dictating the implementation language up front as part of the bounty is a mistake. They should have put the bounty on the speedup factor they're looking for and let it sort itself out.
My not-completely-naive guess is an expert optimizer can get the improvement they're looking for with only small parts or maybe even none of it rewritten in another language.
familiarity. and rust seems to be winning the war for web development tooling, at the moment. zig (by way of bun) may make a good stand if bun were to produce such tools too, as standalone. it’s a high barrier if bun has to be adopted wholesale in order to have a pretty printer.