That's like saying you can't build an e-commerce website on AWS because you're competing with Amazon retail. SpaceX might lose starlink customers in the near-term, but they still profit handsomely from the launch services. Hell, Tesla has supplied batteries to Mercedes and Toyota in the past. If you're a lemon farmer who makes lemonade and a lemonade company wants to buy your copious lemons, you sell them lemons.

It's worth pointing out that it may not even be feasible for AT&T/Google to pursue this venture _without SpaceX_, which means they're making money that they probably wouldn't otherwise make regardless.