Unfortunately, there is a reason for that. Adding new animations into the game is very hard and very annoying. I am not even sure it is possible to make each race use different animations. The way the engine works is that all human Actors (Character, NPCs, etc) use the same animation package. So changing one would make it change for every NPC regardless of race. Also, it is near impossible to add new animations unless you replace others. I know there is the mod FNIS, but it is not as simple as that. FNIS only really works for poses, idles, and stuff like that. There is a reason why there are pretty much no mods like this and the only ones you can find are replaces. Sorry to burst your bubble. A lot of us would love this and have discussed similar things in the past. Sadly, the Creation Kit is just very limited in this department.