Different decal processing. The decals on non-static models (even if they're not moving) is different from a decal on the terrain. Someone will need to locate the timeout for each and adjust them so they stick around longer.

EDIT: Understand that several decisions were made for resource management. Decals use more resources than I would've thought before I understood them.

Would be cool yeah

There might just be something you could do to make blood decals last longer - but I recall that being taxing on hardware for KCD, I think. Corpses last about 24hrs before de-spawned, so you'd either have to make blood decals last the same, or replace the blood decals with something else after they de-render.

I've always wanted to implement a blood trail system for living NPCs/Animals.

It'd have to be a Lua script, I think. Basically the script would "poll" or check for bleeding - say, every 5-10sec, and if they're bleeding, then blood would splash down like when struck by a weapon. It'd have to be a trigger though, cause you couldn't want it polling every single NPC, all the time, every 5-10sec, cause that might be CPU intensive. Though, to be honest, I don't know much about lua scripting. Still, I think it's possible.