The reason is right in the "what's new" section of the T-Mobile privacy policy: https://www.t-mobile.com/privacy-center/our-practices/privacy-policy https://www

The reason is right in the "what's new" section of the T-Mobile privacy policy: https://www.t-mobile.com/privacy-center/our-practices/privacy-policy https://www.t-mobile.com/privacy-center/our-practices/privac... > "However, starting April 26, 2021, T‑Mobile will begin using some data we have about you, including information we learn from your web and device usage data (like the apps installed on your device) and interactions with our products and services, for our own and 3rd party advertising, unless you tell us not to." T-Mobile sells browser history data to advertisers, and Private Relay blocks that revenue stream. They are on the offensive to protect their new-found profit center, and most likely are doing this now to show Apple that this is not a feature that they want to see be turned on by default. It's the beginning of the same saber rattling that Facebook did when Apple announced it would simply ask customers if they wanted to allow apps to track them