Subs Factory has been available on the Mac App Store for a relatively low price since August 2013. Since then, all updates have been completely free, and lots of improvements and new features have been released.
However, in order to be able to spend more time developing this application, it has to generate new revenue.
To avoid penalizing users, existing free features will never become paid features. However, the new translation and transcription features cannot be free.
Moreover, these features use translation and transcription services that are not free for such quantities of data. Hence, it is necessary to pay the translation and transcription services providers.
Using the paid translation and transcription services supports Subs Factory development.