> I don't know why using the default browser a OS comes with or not would be better?

Are being ignorant on purpose now?

Apple's Safari has integration with Apple's Password app which firefox does not. Edge automatically connects with your Microsoft account.

Both browsers sync tabs, bookmarks and so on across your Microsoft/Apple account connected devices.

For a lot of 'average' users this is already extremely convenient.

On top of that, Safari is still the most 'energy efficient' browser you could use on macOS.