From the time I was there, I gathered they hire and fire somewhat quickly. I heard stories about "x intern" or "y new hire", that was let go shortly later. I was also let go after a very short time for unclear reasons. They hire in bulk and keep a very select few. If this is your first job out of college, don't expect to be considered for the long term. They certainly aren't.
This is speculation, but I suspect they hire people with not much experience in hopes they are worth much more than they are paid. A significant portion of their staff consists of younger people (at least the programmers). They keep the top performers and lay the rest to the wayside.