The emails that it is useful to do analytics on and the emails that it is useful to encrypt aren't the same emails. The valuable emails to analyze for a company who sells targeted advertising are the transactional emails - booking confirmations, purchase receipts, etc so they can build up a profile of what your habits are, and it is incredibly unlikely that anybody is going to start encrypting those. The email you send your boss updating him on the latest project status, or a personal email to your parents don't have a lot of marketing value.