Why do AK rifles have removable lower handguards?

The reason is so if you want to put a grip, laser, or some sort of attachment that goes under the barrel of your gun. So if you want to put something under the barrel to help you aim or keep the gun more controllable and stable when your shooting. So if you have a hard time keeping your gun stable when your shooting prone, crouched, or standing put a grip for the standing and crouched possessions, if your going to be shooting prone put a bipod under the barrel to help you aim just note that your not going to be able to turn as easily with a bipod on it the wider the bipod is. Also to allow cleaning like C3 Shooter says and the same with Jeff Carlisle says with "So that the barrel can be oiled.". But both of those guys are right as well.