Why use kites rather than sails?
The biggest advantage of kite power is that pull can be applied to the craft so as to minimise heeling. Theoretically this eliminates the need for a keel or multi-hull type form stability. In practice however, waves can be as big a threat to stability as wind loads on sails, so stabilisation of some sort (keel or multiple hulls) is still required on dedicated kitesailing craft in open waters except maybe for very large craft (say bigger than 20metres).
