Why do elements that make positive ions occur on the left side of the periodic table while those that make negative ions occur on the right?

Because on the right they want and gain electron while on left they give

Metals tend to lose electrons in order to attain an e-configuration isoelectronic with a noble gas; or gain stability in the form of a half or full outer subshell. Non metals gain electrons to gain an isoelcetronic noble gas structure.