1). Systems at higher frequencies can carry more information (data, pictures, channels, etc.) than at lower frequencies.
2). The "dish" antennas used for satellite communication, both on the ground and on the satellite, have more gain at higher frequencies than they have at lower ones.
3). Radio waves at frequencies lower than VHF reflect off of the ionized layers of the atmosphere and return to Earth. They never get out to where the satellites are.
4). All of the communication spectrum (frequencies) below VHF were already being used for other services by the time satellite communication started (in the 1960's).
