May I ask why people think it is okay to fight the lane member they fed constantly?

Usually it is because they want to try and comeback. Or they see an opening they would normally take but forget about the difference in items/levels.

For example they are at full health and the enemy is below half. So they go in for the easy fight but forget they are down an entire item or something.

Also some people just like to keep fighting and don't care much for the farm game.