You are oversimplifying though. It's not just hit 1-2-3. You have to also deal with how large a group of mobs are, you have to make sure they are facing the correct direction when maintaining aggro, you have to deal with the occasional aoe requiring you to move, you have to make sure your hotbar is set up correctly so you can use those skills efficiently, you have to actually know what those skills do, you have to understand what the tool tip is telling you and so on. It's not just 1-2-3. For people like me, it can just be too much.
I am not saying that lazy play doesn't happen. However to think that bad players are ONLY just lazy players is a bad generalization and discredits the claim. It's like saying "Some of these apples have worms in them so ALL apples must have worms in it." It's faulty logic and doesn't support the claim. There may be more factors going on then what appears on your screen.