Because i trust the sound engineer who designed the sound signature more than my own or some audio reviewer’s ability to set a headphone’s sound up well. If i adjust bass i might be losing details in the highs, if i adjust upper mids i might be losing lower mids. Headphone tuning is more complex than 12 graphs. There’s a lot more that goes into good sound than whether a sound comforms to an arbitrary target or my preferences which are largely based on what i’ve listened to before.