Flights to world wide destinations such as USA, Dubai, Australia, New Zealand and Middle east are usually operated by chartered airlines at larger airports who have higher take off / landing fees and hence charge more. Plus the distance to travel (air miles) and fuel costs all add up as well. But for popular routes, larger airlines compete on prices and may offer great value fares on certain routes.
Usually chartered airlines such as Emirates, British airways, Air france and Lufthansa offer special rates for advanced bookings. But these days there is no shortage of flight comparison web sites to help you search for the best available air fare. If you spend a bit of time looking at different sites, you may be able to find cheaper fares for the same flights.