Why not transmit relevant operational data, along with cockpit voice recordings to the satellite, every 60 seconds or something, and do away with the boxes?
The airline companies can record the whole thing and toss them out after a safe landing, or keep them for a week or something.
It's bound to be less traffic than the legions of twits.
Very good questions.
Here are a few reasons:
1. Satellite space segment is expensive.
2. The antennas will not work with the aircraft in unusual attitudes, such as diving straight for the ocean.
3. There are fairly frequent windows of satcom unavailability.
That was proposed after AF447, but, IIRC, was shot down because of the cost of satellite data transmission.
That's probably also why the Boeing Aircraft Health Management messages are limited to just a few significant events per flight.
Redundancy (in the engineering sense).