Simply put, companies building apps have strong incentives to gain more users, even users that derive very little value from the app. Sometimes this is because you can monetize low value users by selling them ads. Often, it’s because your business relies on network effects and even low value users can help you build a moat. So the north star metric for designers and engineers is typically something like Daily Active Users, or DAUs for short: the number of users who log into your app in a 24 hour period.
What’s wrong with such a metric? A product that many users want to use is a good product, right? Sort of. Since most software products charge a flat per-user fee (often zero, because ads), and economic incentives operate on the margin, a company with a billion-user product doesn’t actually care about its billion existing users. It cares about the marginal user - the billion-plus-first user - and it focuses all its energy on making sure that marginal user doesn’t stop using the app. Yes, if you neglect the existing users’ experience for long enough they will leave, but in practice apps are sticky and by the time your loyal users leave everyone on the team will have long been promoted.