Tldr: it's a metric fuckton of work and unlikely to happen.
Longer answer: the animation in this game is primarily done using layering. As in you have an image model, and then you have each other aspect of the model - lets use Kotone for an example. She has a bunch of default models, but she also has a bunch of different faces, different tails, different clothes, et cetera. Aany picture with her has at bare minimum a tail pic, a face pic, a body pic, and a clothes pic. Many also have arm pics or her gem, or special lighting, you get the idea.
For each of those "animations", you have to make sure everything is properly linked up, so you don't have someone ahegaoing when talking normally. As of 25.9 kotone has 203 images in her set. Even if you gave each character an eigth of that, it's still so much more work than is at all reasonable.
As such if they do add animations to other characters, it'll likely either be after the story is complete or as side projects/reworks like Nicci and the mimics.
As for why they don't have individual loss scenes, same issue. It's a ton of work for something that is less impactful than a new story expansion.