The main reason is availability ( I almost never see carbon clincher wheels listed where I live) and also weight.

About the fragility of the disc wheel I was mostly thinking about potholes, I understand that every disc wheel will be very fragile on the sides.

The FLO disc is around 1000$ before VAT and shipping, plus its a wheel cover above a spoked wheel isn't it ? and it weights 1300g, that's as heavy as my current front + rear combo.