Game doesn't magically know whether or not there are hostiles left, and the situation itself is subject to change. You killed a squad in range, but a new squad might have just landed on your square, for example.
It's not really, though. If it is removed you can just continually hammer on your opponent for ten minutes until he dies. This way all of your shots are spaced out, and unless he's offline for a day or more he'll likely be able to hold his own for a while in an equal 12v12 match. I have heard no plans of removing the fire delay nor would I think that would be a good idea.
Honestly, from the way this one understands once the aggression aspect of combat is implemented with npc's, such as creatures, would that not naturally mean they will get time to move, get into range, run or initiate combat as well during your time delay?
For example if you are shooting bandits and a rancor comes into range and decides to attack that would be the same thing as Syn just mentioned with enemy squads appearing to attack you. Basically, the time delay would be there so that others that see you can attack. If the ending time delay was gone you would have the first attack on another group rather than they having the chance to attack you first.
This one has always taken the time delay after battle to represent time needed to recover from battle considering chances are you and your allies have taken damage would be nearly certain. This ones opinion only of course.