I will answer with quasi statistics. I got the actual numbers about 2 years ago in a translation conference.

You can apply this answer to interpreters as well as translators.

The answer is this, in a nutshell:

Even though the percentage of documents that need human translation is drastically decreasing, the total number of written text worldwide is increasing exponentially faster; At such a high pace that there is an EVEN HIGHER demand for language professionals.

To put it in numbers (just as an example, since I do not remember the exact statistics and hence I cannot quote them):

Lets say that up until the year 2000 there were in existence through human history a total of 100 pages of written text. Including every book and newspaper ever written. And say 10% of that required human translation. A total of 10 pages.

But now, given our current technological advances and the enormous amounts of data generated in blogs, emails, text messages, news, movies, and general data, we generate the same amount of text (that took millennia to write) in a matter of weeks.

So instead of the 100 pages, lets say we now have 10000 pages of written text. And since machines are taking over a large portion of that, and lets suppose that instead of the prior 10% that needed to be translated by a human, we now only need 1% to be checked by human eyes. That gives us a total of 100 pages for humans to translate. 10 times more than before.

In this, very crude example, I am illustrating how, even though machines are doing better, there is an increased demand for humans. Projected to be about 17% (increase in demand for human translators) in the next 10 years or so.

Again, my numbers may be WAY off, but the concept was the same. That’s what I gathered from the conference I attended on behalf of Legal Translations, Inc..