unlockers are rarely customers of original carrier
i have worked at a few different shops that unlock phones and also helped many individuals with unlocking. the reality is that people wanting to unlock phones they own are only very rarely customers of the carrier that sold the phone and able to get unlock assistance from them.
most phones people seek to unlock are purchased second hand for use on prepaid or purchased for export, the second largest group would be people who have already left their original carrier and no longer have access to there customer service but now want to use a different carrier.
at&t does not help these people, they will help the customers that want to temporarily use a local sim while traveling overseas but i would guess this is only a tiny number of people compared to those who want used phones unlocked.
at&t should at least offer a public website where anyone can input an IMEI number and if the phone is eligible(past the contract term or was purchased outright to begin with) get an unlock code. this service should be available equally to customers and non-customers alike.