I think an economist would tell you it is human irrationality. However, I think there are a few factors - a big one is that a change is as good as a rest. Doing 40 hours development and 10 hours running errands is a nicer balance than 50 hours development, and probably with similar productivity. There's an overhead to hiring help too - setup and management. You're also becoming more removed from everyday life. That might be a benefit or a drawback.

That said, I recently hired a servant to take care of all those things that I don't like to do (I live in a low-wage country). Shopping, Cleaning, Laundry etc. About $400 a month, although it could be a lot less. Wouldn't go back.