The reasoning boils down to Google-ability.

sh is not a distinct enough term when googling for shell suggestions, because both cheat and cheat.sh will have sh in the results. That is very distinct from xterm.js where xterm-only results are very unlikely to have JS in them.

A similar debate played out when the gofish package manager was launched, which conflicted with the fish shell https://github.com/fishworks/gofish/issues/37

Anyway, the choice is not mine to make, it just seems like an easy issue that could have been avoided by choosing a name that wasn't already in use.