I think one of the main problems is that a surface-level argument can easily be made that user engagement represents the quality of the user experience (i.e. "u

I think one of the main problems is that a surface-level argument can easily be made that user engagement represents the quality of the user experience (i.e. "users that spend a lot of time in the app clearly like it"), despite falling apart if you dig deeper than the surface. The allure of short-term profits makes such an argument attractive to upper leadership. It also makes it more difficult for a lower-level employee, like a designer, to convince them against it without direct evidence that optimizing for user productivity is better than optimizing for user engagement. Combine the ease of making that argument with potential financial incentives to the designers to optimize for that, then you get relatively easy conformity to that goal. I'm sure there's plenty of designers that will happily accept it, so as a company, you can easily replace any designers that push back.