Please explain the main physical advantages of using satellites for communication as I'm sure there are many.
This technique is only good for frequencies below about 30MHz, and tend to be omnidirectional (depending on antenna). This limits the amount of information that can be encoded and transmitted between specific Tx/Rx pairs. Satellites use tightly focused beams in the tens of GHz, providing far higher bandwidth and more discrimination between data paths.
Bandwidth, and a more specifically amount of information you can send within it is crucial. Satellites are used for video transmission (DVB-T2), audio communication (Inmarsat), data communication (Internet link) and all of this within one hardware box.
Jamming. This is the crucial issue, imagine 1000 people communicating with each other in the same channel, earth effects, sun effects. Even if coded data will propagate within your signal, you will need advanced techniques to reduce SNR.
Coverage. Time of propagation between satellites is much lower that within ionosphere. Imagine you want to send data from the UK to Australia, it will take several ,minutes to propagate and seconds within satellite constellation. Earth-Ionosphere propagation takes at least twice more distance