Smartphones and dongles are omni-directional, which means they have the potential of tying up a slot/frequency on multiple towers at the same time. Presumably these cans are directional - aimed physically or electronically at a single tower. This reduces the impact on the wireless part of the link which is the part that's limited. By going directional, they can also increase the gain of the signal between the house and the tower. My guess is that they do that passively by the antenna design rather than increasing power. That's why the cans are as large as they are. They can't boost the tower power or the house power as that would cause problems for the mobile users.