According to their privacy policy, Crashlytics aggregates the data that's being collected in every app. "Crashlytics does aggregate information across Develope

According to their privacy policy, Crashlytics aggregates the data that's being collected in every app. "Crashlytics does aggregate information across Developers in a non-personally identifiable way. Such aggregate and anonymous information is used by Crashlytics to (i) improve the Services, (ii) create analysis of trends or behaviors and (iii) other similar uses, but always in an aggregate and anonymous way." Knowing what apps are trending probably helps Twitter to make decisions on what to focus on next (like with the Meerkat / Periscope apps, and their acquisition of Periscope). That data should probably be enough for Twitter to keep it free for now.