What's with player attack move click when target champions only is on?

So when you use "player attack move click" when "target champions only" is on and you click near a minion it will target minions instead of the champion next to the minions if you click closer to the minions.

This would be fine if it remained consistent.

In the same scenario as before but with monsters or scuttle crab you actually won't attack any of those things. Your character will not attack them (the jungle monsters) at all using "target champions only" and "player attack move click."

Is there a design reason behind this? What's the point if so? I feel like you should either not be able to attack minions, or you should be able to attack monsters like this.

Can anybody elaborate? Does anybody know what I'm even talking about?