"He speaks as though he knows everything."
Translation:Er spricht, als ob er alles weiß.
I think it's because "like" is just not quite the same as "as if" or "as though".
As "like" becomes more and more an everything-word ("He was like 'duh'. And I was like of course. And like he said he like doesn't like to like it. . . . . . ") I suppose the distinction will disappear. Unfortunately.