Why do minions deliberately change their target to last hit other minions?

Copy-and-pasted! (You know, you can search your question instead of posting a new thread! Not that it's a bother, just letting you know in case you might've found that easier ^.^.)

I believe it's cause by the minion distress call system

so y'know how tower agro works right? If you attack an enemy champ (or deal damage to them in any form, especially dots and also zileans bomb) while under the towers range, the tower starts hitting you?

well minion ai that will attack enemy champions and other minions that have auto-attacked nearby allied champions.

But it doesn't stop there, it will also "help" allied minions under attack by other minions, causing them to switch targets, and quite obnoxiously to me (and probably to you too OP, based on your post), it has a high tendency to switch to the low health enemy minions so I miss CS.

edit: here's a link to the wiki http://leagueoflegends.wikia.com/wiki/Minion (Man this takes me back, I haven't seen this post since I started playing in Season 3 and was really interested in minion/tower AI rather than exploring champs) But here's the important part:

Minions prioritize targets in the following order:

An enemy champion designated by a call for help from an allied champion. (Enemy champion attacking an Allied champion) An enemy minion designated by a call for help from an allied champion. (Enemy minion attacking an Allied champion) An enemy minion designated by a call for help from an allied minion. (Enemy minion attacking an Allied minion) An enemy turret designated by a call for help from an allied minion. (Enemy turret attacking an Allied minion) An enemy champion designated by a call for help from an allied minion. (Enemy champion attacking an Allied minion) The closest enemy minion. The closest enemy champion. unfortunately, the wiki tells us also that it "checks" every few seconds- there's no actual set time that has been found that can be used so one can predict the ai's targetting system a bit better. Perhaps it's intended design that it's too difficult to find; a way to create variance in a relatively harmless way to encourage the player to pay attention and test their ability to react to the differing issue.