It automatically places the actors because the actors are placed automatically by RPG Maker. The enemies in a troop are placed by the user. So their visual location is determined by the troop setup.
But the point of the enemy row tags isn't to set their visual location, it's to set gameplay options based on row locations.
Let me try it this way. When you're setting up rows for actors, they change their locations. But that's not the actual purpose of setting rows. The purpose is to have the gameplay different for each row. So, actors in the front row can use melee weapons and can target the front enemy row. The second row uses ranged weapons, can target the front two enemy rows, and take less damage. The third row takes hardly any damage, but fights slower and can use magic to attack any enemy.
It's *those* settings that will be applied to enemy rows. It's just up to you set them how you want them visually.
The reason it doesn't automatically set them is to give you creative control. Keep in mind that rows work with normal enemies, not just animated sv battler enemies. Enemy pictures are all different sizes, so automatically sorting them would be a nightmare.
I hope this helps.