>>214472394
The real world answer: George Lucas didnt like showing people being killed, even when you couldnt see the people because they were in stormtrooper armor, so shooting and slicing droids was much more kid friendly.

Since the Jedi were going to be a huge part of the prequels, he had to show them actually slicing things, so slicing droids with lightsabers is much easier for a PG rating.