Human translators are so expensive today that they are only used in situations where the translation has to be correct -- diplomacy, courtrooms, books, etc. Until a machine is much better than a human, these use cases won't switch to machine translation (similarly, self-driving cars won't be allowed until they are proven to be much safer than human drivers).
On the other hand, there's a large casual market for machine translations today for situations like reading foreign Web sites, chatting with people in different countries, reading Tweets in a different language, etc.