There are many satellites overhead at any given time (the current LEOs and MEOs usually have just one), so terminals need to be able to limit their gain to a small angle not only for gain reasons. Steering in handheld applications seems very difficult.

Of course, they could dedicate parts of their spectrum to "one sided beamforming" and compete with Iridium that way (no idea if the L-band has any other advantages over Ka when used like that).