fish, the friendly interactive shell, is a commandline shell intended to be interactive and user-friendly.
fish is intentionally not fully POSIX compliant, it aims at addressing POSIX inconsistencies (as perceived by the creators) with a simplified or a different syntax. This means that even simple POSIX compliant scripts may require some significant adaptation or even full rewriting to run with fish.
Honestly, I didn’t see it that way. With the dash, I do. That works as well. It’s just that, if I put a dash somewhere myself, it’s the other way around.