It's only been 9 games. I know that the offense has been an issue, but to start reshuffling the deck at this point is rather premature. Calling up a very important prospect because of it is as well. Plus, he needs the reps at SS and he's clearly not going to get those while Correa is healthy.
And after not playing for 2 years, Lewis has only played in 10 games. While his performance is encouraging so far, that's hardly a large enough sample to say that he's ready.