I used to play Company of Heros and that game does use a kill count for how many and what type of units were destroyed. You usually command about 5 infantry squads and maybe 5 vehicles at once at the most. The small number makes each important and you should be attached to them. They also level up. Then there's Sins...hundreds of units all firing at once in massive space battles - how would kills be awarded when all the damage is being shared amongst that many ships? You could do it by % damage dealt but it still seems silly, sorry. I'd be curious how many ships my capitals and Titan have wiped out over the course of a game but don't really care for frigates/cruisers. I think this would be much more work than it's worth for the devs and there are other far more pressing (balance and bugs and new maps) things that need attention already.

First off, all units need to have another integer variable attached to them.  This is likely an easy change.  Then, you need to figure out last-hits which the game does not currently do.*  That's more complex but not hard.  Then you have to display it.  That means a change to the UI to accommodate a new variable and possibly even a new draw function.

Because there appears to be some funkiness with buff chain tick rates (and possibly the tick rate of the engine itself), last-hits may not be possible.  You'll have to be sending a pointer along with all your shots.

None of that is a ton of work (unless the Iron Engine is really weird), but still..  They have more pressing issues at hand than this.