For jobs, but also for many other things. It's where lots of things come together, lots of things happen. More restaurants, museums, night life, music venues, theatres, etc. Cities often have a long history, historical landmarks, etc.

I certainly wouldn't want to trade Amsterdam for the town I grew up in. Then again, my dad clearly disagrees. On the other hand, Amsterdam probably isn't quite as expensive as London, New York or San Francisco.