The Developers don't like the idea that, due to some bad random numbers, you could be becalmed or unable to reach port for an extended period of time. At the moment, the inexorable rotation of the wind is to ensure that, for a majority of the time, you have wind in a direction that will work for where you want to go, while still forcing you to sail and beat up from time to time. Having trades, or other systems that prevent you from reaching your destination for a long period of time would, naturally, cause a lot of rage amongst players. Hence, for now, the auto-rotating wind is a compromise to playability.