Battle Droids are the incompetant footsoldiers of the CIS. Cheap and easy to manufacture, the droids were designed to attack in huge numbers and swarm enemy forces by sheer numbers (rather likethesefools). In fact, the CIS only used Battle Droids for a number of years, only at the start of the Clone War did they decide that a more advanced commando was needed (namely the Super Battle Droid).
After the downfall of the CIS, the Battle Droids were rarely seen again. They had proven their uselessness as soldiers and their quirky, child-like programming didn't help either. Most people just found them annoying, especially retired Clone Troopers.
A pre-Clone War Battle Droid deployment
Battle Droids fighting alongside Super Battle Droids