The radio bands allocated to aviation are very limited and are being constantly eroded at every International bandwidth allocation meeting. Some years ago we were forced to reduce our VHF Communications to 8.33 KHz channel spacing to enable us to have enough available VHF frequencies. That is not a misprint - radio channel separation is about a third of the audio bandwidth of a decent Hi-Fi system. Imagine how tricky it is to prevent cross channel interference in such a tight channel space - the audio modulation is reduced to around 6.7 kHz! Meanwhile, global telecomms companies are after even more of the "under-utilised" frequency bands allocated to aviation.
All these people proposing real-time data telemetry of aircraft really have no comprehension of the technical difficulties involved in airborne communications. Bandwidth is limited and allocation is a regular bun-fight with everyone wanting to earn profits from grabbing a share. We already lost one entire band to cable television, for broadcasting Pap to the mass market. The frequency band currently used for Mode S/TCAS is being demanded for commercial use by telecomms companies.
Real time telemetry would involve something like a constant stream of 30 Mbs for each of possibly 400 aircraft in a ground footprint on the channel in use. Where do we get the bandwidth for that? Propose such a thing at the next international radio band allocation meeting and you'll be laughed out of the room. It's hard enough holding on to what we've got.