[@Akayaofthemoon] I have a hypothesis that it's a combination of Garen being the champion you play as in the tutorial, being a fairly low entry level champion in terms of skill, and being a tank.  New players will assume that 'tank' means 'pretty much invincible' like it does in MMOs so they can run in without any assistance.  Garen players who feed are like an environmental hazard or something.