Well, there have been a few instances in the past where I've been desperate to hire and I've brought people in against my better judgement. I can tell you it sucks having to look someone in the eye and let them go because they couldn't keep up with the rest of the team. Once you've had to do it a few times as a manager, you become more conservative with your hiring.
Sure, pushing pixels around is easy, but when you're up against a deadline and the app is crashing in a subtle way, you need engineers who have solid debugging chops. Not everybody does.