I guess it has a lot to do with immigration procedures. Years ago in Hangzhou it happened to me almost the same (it was during the passage of typhoon Sam in HKG and the accident with the taiwanese DC10 that forced airport closure). We had to wait from 3PM to 9PM with minimal information given until KA told us the flight was cancelled. In the meantime they had PSB to reissue temporary visas to those in need to allow all passengers to be accomodated back in Hangzhou for next day flight. KA probably did try its best to leave and avoid the hassles of such dealings.