One reason it is so expensive is basically the same reason it took so long to become available and that is so many different agencies have control of various aspects of international travel and communication. An airline cannot just decide to fly between two airports. IATA, the state department, the FAA and several others are involved with the US part of such. For communication there is ARINC, the satellite owner, various government agencies, etc.
SATCOM became available for the airlines to transmit position reports over the vast Pacific many years ago but for at least a year or two, they still had to officially use the HF for clearances. HF is potentially very unreliable and the Pacific traffic really tied up the frequencies. During this interval the airliner would get his clearance over SATCOM and the "verify" it over HF. Silly, but true.
The bottom line is the technology for pax internet service has existed for years but all the politics kept it from happening.
Best regards,
RA1