Some apps have lower profit margins than others. Also some companies need to be able to integrate with their realtime channels on the backend (E.g. for doing custom realtime analytics, integrating with third-party services, applying transformations/filtering to messages in realtime, capturing certain messages for storing in your database, launching various realtime-based background tasks, etc... You do lose a lot of flexibility by going with a service like Pusher. Though it is well designed and very convenient.)