I left about a year ago and it came down to just feeling stifled in my job. There was a hiring freeze and "cost containment" i.e no training budget. I wasn't really feeling challenged in my job and my skills were getting stale. Combine that with the fact that pay is just perfectly average. Promotions are very hard to come by, and you get caught up in the HR grinder that happens at many huge companies. You have no idea if you are doing what you need to do to advance or not. Looking back, leaving was the right decision.