"Arcane" means "requiring secret or mysterious knowledge". I think there are quite a few features of bash that qualify as arcane. I've been writing shell scripts for decades and I still have to look up how to do certain things often enough.
And if you want to write in portable shell, remembering all the rules and things you can and cannot do feels somewhat arcane to me.
And if you want to write in portable shell, remembering all the rules and things you can and cannot do feels somewhat arcane to me.