Why should we use LED driver chips instead of much simpler structures?
Another good reason is the driver's efficiency: -



It's a current limited switching regulator there fore there is hardly any power lost in current limiting resistors or transistors unlike the other three circutis shown in the question. Here's ahow the data sheet describes the chip: -


  With the internal 500kHz operating frequency, the size of the external
  PWM inductor and input/output capacitors can be minimized. High
  efficiency is achieved by a 100mV current sensing control.