Why bother with complicated satellite connectivity when you likely have a smartphone in the pocket? For one thing, the FCC has banned the use of cell phones aboard aircraft per 47 CFR 22.925 l. Originally, it likely had to do with the way the cellular system works.
As the name implies, geographic areas are divided into different cells which use different frequencies, and no two adjacent cells use the same frequency, but two separated cells can safely share them. A phone in a plane has a much longer reach than a phone on the ground, so it could tie up a single frequency across multiple cells. Furthermore, the phone may not be able to receive a signal at all with multiple cells using the same frequencies.