Yes, there was the bourne sh on Unix but I don’t see how that’s relevant here. We’re talking about operating systems in use. Please explain the downvotes

There is no sh shell. /bin/sh is just a symlink to bash or dash or zsh etc.

But yes, the question is valid why it compiles specifically to bash and not something posix-compliant

I really hope they also license the code under the AGPL, otherwise the product would not be as good as mastodon in my opinion. See https://ploum.net/2023-06-23-how-to-kill-decentralised-networks.html