Even so, judging from my limited experience of DnD 3E by playing the Pathfinder cRPGs, effectively unlimited AoO -was- possible there if you built yourself for it, but there were also a lot more conditions to trigger them AND avoid them too. (In those games, you took opportunity attacks for each spell you cast or arrow you fired with an enemy next to you, so long as that enemy had enough available opportunity attacks to punish you for it. It appears that got replaced with disadvantage in 5E instead. You also used to take an opportunity attack when standing up from being prone, but no such penalty exists in 5E.)
In D&D 3.0 (not sure about 3.5 and Pathfinder) it was possible to make multiple AoOs, BUT it required a feat (Combat Reflexes) and even then was limited by your DEX modifier which heavily impacted it's usefulness for anyone wearing medium or heavy armor. Also, you were still limited to only one AoO per enemy of course.
