It isn't!!! The only problem is that you do not benefit from the Earth's rotation to give your space vehicle a free boost into orbit. This is why we launch as close to the equator as possible, and launch towards the east which maximizes the speed of the rocket because it gets a free 1000 mile an hour boost. Putting a space craft into polar orbit requires that you expend extra fuel to boost a satellite into orbit which of course costs money and takes up extra weight for the fuel. There may be other technical issues at work as well, but I am not an astrodynamicist! If anyone out there knows something about this, please let me know!!