The standard text boxes on macOS don’t use readline, they use NSText*, which happens to implement similar things to the defaults for readline (because they were

The standard text boxes on macOS don’t use readline, they use NSText*, which happens to implement similar things to the defaults for readline (because they were created by people who used Emacs a lot, and readline defaults to Emacs style). This is really only important because readline customizations won’t affect macOS text boxes — but it will affect readline programs on macOS, including bash.