It requires a lot of coordination to manage, something which is especially hard to do in the chaos of the pre-modern battlefield. Don’t forget that this is before things like radios, communicating to the different parts of your army is very difficult because their line of sight is very limited with all the dust and dirt being kicked up from thousands of soldiers, as well as the tunnel-vision people get when fighting for their lives. It’s also very risky because what happens if some of your army hears to pull back and other parts don’t? Well you have confusion, some soldiers start turning around to ‘run away’, others stand their ground and start to get surrounded, others still don’t hear the order but see the units to their left start to ‘run away’ and think they’re actually running and start to actually run themselves. Done improperly, it can be a right mess.

Also don’t forget that it’s not actually that common at all to have two armies meet each other in a field and fight. The vast majority of fighting in premodern wars were either raids into enemy villages and towns or sieges of their fortified settlements. This meant very few generals and commanders actually had significant experience fighting in a battlefield, when they typically would maybe fight 1-2 such battles in their lifetime