why do we need a driver for laser diode? what is wrong to connect it like an LED since it seems it works.
What is wrong is that the forward voltage drop of a laser diode is not as stable as an LED. So to run the laser at anything close to full power you need a much better current regulator than a simple resistor.
Sometimes this involves optical feedback where the current is adjusted according to the brightness of the LED.
Also an over voltage to a laser will kill it very quickly where as LEDs are very much more tolerant of this.
The "it seems it works" sort of evaluation is not good enough to provide a reliable, long lived piece of electronic equipment.