Why are microwaves preferred for satellite communications?

Frequency of microwave bands extends from about one gigahertz to three hundred gigahertz. This large frequency bandwidth can carry huge information through different band.

Velocity = wavelength x frequency

From the relation we get they have short wavelength.

Due to enough short wavelength, they less capable of bypassing the obstacles of dense media like walls, hills etc . But it is a matter of think that microwave propagate through less dense media like atmosphere, free space in satellite communication.

Large frequency signal can convey large power and less attenuated. This leads to an essential property of microwaves is that they travel in straight lines through the atmosphere (like a torch light), are not affected by the ionized layers. So they can travel long distance. 

Also these waves are very less affected by temperature inversions and scattering. But these weather effects limit the distance between the transmitter and the receiver to a few miles. This problem is overcome by usage of repeater stations placed along the propagation path. As they do not rapidly disperse in the atmosphere (less attenuation) so the power does not need to be very high to reach a distant point.

Because of penetration and traveling property, main mode of propagation in the microwave range is line of sight. Line of sight means that the transmitter and receiver need to see each other. That is the prime destination of satellite communication.

Generation of microwave is not complicated. Simple devices like magnetron can be used. Using metal reflector antennas, they can be easily directed from earth to satellite and vice-versa. 

Various modulation techniques are available for microwave. So possibility of interference among data is very low. Due to large frequency bandwidth, a huge number of variable services are available without blocking.