While the wind characteristics can play a part very occasionally, the runway operating policy of departures on the south and arrivals on the north is primarily to ensure independent operations under the vast majority of conditions.
The ICAO guidance for independent parallel runway operations recommends 30 degrees divergence between a departure from one runway and the missed approach track of an arrival on the other.
Due to the terrain around CLK, we are limited to 15 degrees divergence, if an acceptable minima/climb gradient is catered for, however the runway spacing at CLK is approximately twice that required in the guidance.
A safety case was carried out, based on, in simple terms, twice the initial spacing and half the divergence, (its not quite that simple obviously when determining the tolerances, especially in the MAP phase). The risk was shown to be no worse than the ICAO guidance.
Obviously if we reversed the runway operations we suddenly have a situation where the south runway MAP has to be straight ahead due to Lantau and every departure off the north runway would have to turn away to the north and somehow get back south at some stage. Off 07 that would be up the Tai Lam gap and off 25 you would head up the PRD- but to no-mans land.
Once the PRD airspace is sorted, well........ Don't call us, we'll call you.