The trouble is when removing the block, one will have to check all siblings to see if the material was inherited only from the single point that was just removed. Yes, still not up to Root in general, but a much larger computational overhead.
Caching up to the eight corners of AABB for the entity collision, versus caching a single point location, to avoid traversing from Root to find world blocks at the entity’s coordinates makes a lot of sense for large worlds. Bit of memory vs search balance there, and relies on how easily siblings are linked for the search.