Even at the speed of light, radio waves take a noticeable time to get there and back. This time delay used to plague international phone calls, but has now largely disappeared as they are routed over fiber instead. Second, the geostationary orbit only works around the Earth's axis of rotation, the equator. This has become very crowded, creating a risk of radio interference between satellites. Equatorial orbits also make satellites difficult for people to use at latitudes in the far north or south.
All satellites require a clear line of sight to their receivers.
This sight line can be blocked by buildings if the satellite lies low on the horizon. A geostationary satellite typically spreads its beam over a very wide area, perhaps nearly half the Earth's surface. Away from the equator, passing through a thick cross section of the atmosphere further reduces signal strength. Just as colder parts of the Earth receive little of the sun's heat, they receive little of the satellite's transmissions. So the further north or south of the equator a receiver is, the larger the dish required.