There is an EQ for the Music app, but it only has predefined presets. It doesn't allow you to customize the lows, mids, or highs on a somewhat granular level like the new AirPods equalizer does. So it will likely be more useful to people than the predefined presets. Plus, the AirPods equalizer applies to all apps, not just Apple Music or one's local library. So that by itself makes it far more useful than the EQ setting in Music settings.
Respectfully, why does this matter? Also, you can use what you want but not everyone is you nor do they have the same mindset as you. Not everyone likes to use Microsoft or Google products, so to have the alternative add features that other things have, makes it easier.