While at peak current, the efficiency of a voltage divider is the same as a linear regulator, at lower currents a voltage regulator has significant benefits. 
This is because the quiescent current used by an unloaded voltage regulator can be very low (500nA for the TPS783!), while for a voltage divider to be sufficiently &quot;stiff&quot; its quiescent current should be about 10X the max load current. 
As a lot of microcontroller applications alternate between a low sleep current (several uA) and bursts of high run current (several mA), a voltage divider is significantly (&gt;10000X!) more power hungry then a linear regulator in practice, even if the worst case efficiency for both is closer.