Isn't zsh the current #!/bin/sh on MacOS?

Why is this written for bash, which isn't getting recent changes?

Compatibility with older devices that aren't eligible for recent OS updates, I would assume?

Or, if the person is like me, they're more comfortable in Bash after years of it being the default. Hacking around in a less-familiar shell seems like a bad idea if it's optional when deleting data, regardless of what's currently the default. (I realize that zsh can execute commands with Bash syntax, that's not my point.)