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In 1945, Arthur C. Clarke first proposed the use of equatorial geostationary orbits (about 35,786 km above the Earth) for communications satellites. It took the form of a letter to the editor in Wireless World magazine entitled "Peaceful Uses for V2": lakdiva.org/clarke/1945ww/… 
GEO orbit solved a tricky problem since a satellite otherwise does not remain stationary above the same spot on the Earth. Once satellites are moving the ground antenna must track them which can be done mechanically or electronically. Mechanical tracking requires two antennas.
Lower cost and weight electronics + lower launch costs means constellations of 100s of satellites at far lower weight (e.g., 500 lbs) a low orbits can create continuous coverage. The critical factor then is electronically steered antenna cost and form factor (e.g., pizza box)
