Actually, Riot did answer this question a year or so ago.
The problem with this death recap is that it existed way before Riot started implementing new systems and new champions who have scripted skills that calculate their damage numbers off various different triggers that happen in game. Which means that death recap itself can't pull these numbers accurately as there are no methods to do so, so Riot has to code it manually. But even this has limits and can't be done properly as everything then has to be patched over the existing code, resulting in spaghetti that tends to break even at the slightest disturbance. If you just pile and pile new code on top of the old, faulty one, the foundation can't simply work properly and with every new addition, Riot literally risks destroying the entire delicate system. And when it's broken, it has to be fixed immediately.
Riot did some cleanup work at that time and they improved accuracy quite a bit but it still isn't up to the standards they'd like it to be. At that time, Death Recap wasn't on their priority list and they wanted to fix it. As of now, i think they have other projects so i don't think they would be talking about it at least till preseason is over.