Big advantage for kite is the fact that the equipment is very compact. When you live in a little flat in a big city, you have simply no choice. Windsurfing equipment is such a pain in the ass to transport... That's why so many people quit...
After, in the water, I think windsurfing is better from 0 to 12 knots and above 20/25 knots, in the middle, kite looks more fun (I don't know, I have never tried kiting but it is how it looks like to me) unless you are a crazy slalomer or you have big waves with medium wind on your spot.
It is true that total beginners manage to sail with the kite after one week, which is unthinkable with windsurfing (I mean planning sailing, straps and harness): the people do not want to bother themselves and go for kiting.
Why did I never turn to kiting? Because I still have so much things to learn with windsurfing that I want to work hard to achieve the maximum in this sport!