Excellent comment. I'd say there are at least three possible answers to the question you pose at the end of it:
1. As another commenter replied, Big Tech will have to start charging market prices for their services.
2. Big Tech will be unable to charge for their services, and the business relationship between them and their users will collapse, taking Big Tech with it.
3. The relationship between Big Tech and its customers will change from a business relationship to something else, where the truism you stated will no longer applies.
One might argue that (3) has already happened, and the "something else" is more like a manorial or totalitarian relationship, in which the interests of the users are irrelevant.
1. As another commenter replied, Big Tech will have to start charging market prices for their services.
2. Big Tech will be unable to charge for their services, and the business relationship between them and their users will collapse, taking Big Tech with it.
3. The relationship between Big Tech and its customers will change from a business relationship to something else, where the truism you stated will no longer applies.
One might argue that (3) has already happened, and the "something else" is more like a manorial or totalitarian relationship, in which the interests of the users are irrelevant.