Why is minion targeting in this game so inconsistent?

For how much minions can actually do during laning phase, why the hell do they act so completely asinine?

Sometimes they attack when you poke. Sometimes they ignore you altogether. Sometimes they attack you because a nearby minion died. Sometimes You're literally just walking back from base and they switch to target you. Sometimes when they aggro you they stop almost immediately. Sometimes they won't goddamn quit until you leave the screen. Sometimes they will follow you out of the lane and into river before their aggro stops. Sometimes they bug the fuck out and stand still not attacking anything at all.

For something you see for such a massive part of the game, why the hell are their mechanics unfathomably stupid?