Um. Tmobile has a lot of customers who want an iPhone so bad that they are apparently buying unlocked or used versions. They are the 4th largest carrier which means they have a lot of potential iPhone buyers. Apple might want to sell to that hungry crowd rather than pointing them to Android or elsewhere.
If I'm not mistaken, Tmobile has more customers than a number of countries that are getting/has got the iPhone. Apple apparently cares about even the smallish numbers of potential buyers in those countries. Why not Tmobile too?
This should not take the well-worn frame of <any other company> (Tmobile in this case) vs. Apple. This is a company wanting to help sell more of an Apple device(s). They are NOT the enemy. They want to offer the iPhone to their millions of customers. See it for what it is (which is not one company is totally wrong and Apple is all in the right). This reads very much like if Apple would let them have it, they would sell it to their base.