That quantity of figures on the field (both dead and alive) is an ideal situation which may only be possible by taking away something else that's considered more important. Example 1: Taleworlds allows 1000 corpses on the battlefield, but as a result you can only have a maximum of 100 live troops on the field. Example 2: 1000 corpses are possible if you reduce terrain to the absolute minimum, so you end up with cartoon trees and simplistic castles and town scenes. Example 3: after around 500 corpses, the game drops to a slideshow, and you get severe stutter, making combat increasingly difficult for the player, but it will allow up to 1000 corpses....you just can't fight it yourself because of the appalling frame rate.
Everything is a tradeoff, and dedicating computing resources to one thing means taking them away from something else. It would be nice to have, but I'm not willing to give up a lot of other stuff for it. To me, having 100 corpses on the map is sufficient to show "carnage", without having heaps of bodies 10 feet high at the top of a ladder blocking movement. I do think the game should prioritize retaining corpses in the vicinity of the player, and only remove them as necessary to maintain graphics settings at the minimum specified frame rate. Having corpses suddenly slide across the field and into the ground while you watch is immersion-shattering. I'm willing to allow the developers some leeway on things before I complain, because you simply can't have everything with limited computing (and programming) resources.