Let's say there's a runway 2500 meters. On dry and good reported action the table only gives me AB2. Let's assume AB2 calculation gives us 2600 meters. I can guess that AB3 will work for me. But it's not in the table.
In such condition as I can't set my autobrake depending on assumptions I need to set my autobrake to max or I'll decide on manual braking. Doesn't make sense at all.