Probably because there aren't alot of large and established sensor manufacturers to choose from. Most of the PnS cameras are using one or the other manufacturers' CCDs.
BTW, anyone can buy the sensor from Sony but only Pentax managed to clinch the award.
The Key Success Factor wasn't so much the low noise (which mattered to people like us) but the many cool colours available (which mattered to new customers looking for something different).
Use a white Kx on the streets and you have alot of people looking at you. Try that with a black C or N camera...