Ew, why would you do that? And even more, you seem to forget that you're a bird. And as a bird, your turds are white.
Also, the box contains more than just dust. It contains also those ancestors' favorite items. You aren't quite sure what this ancestor, "Nike" or whatever their name was, did in their life, what they liked, or what kind of person they actually were, but you doubt defiling their corpse would be a good idea.
Now, you have no quarrel with your ancestors at all, you think they did whatever they thought was right at the time that they did it. However, you do have a quarrel with burying dead things with items of or not pertaining to value.
Say your grandfather had a watch that he promised he would give you when he died. And then he goes ahead and kicks the bucket and rap on pearly gates. In the chaos that ensued after his death, the watch was seen by the people of the family, specifically the ones narcissistic and nepotistic enough to only care about the money, as an unimportant thing, that the deceased cared about, so therefore it belongs with the aforementioned deceased. In the end, you are left watchless, your family members (excluding you) grow richer, and your grandfather doesn't fulfill at least that one wish.
Now, that hypothetical is an exaggeration, it was made of pure imagination, but the concept still stands. Burying items with the deceased is a great way to stay in the past instead of bring them into the future.
Now, contrary to that last statement, if you were going to get the watch, you too would probably hold it against the future generations, say, giving it to your own grandchildren, making it an heirloom, which is almost entirely past facing, but I digress, you still don't think burying items with dead should be a thing. That is why when you go ahead and die, you want everything you own to be split between your immediate family, and the thing that killed you. Splitting would be 35/65 favoring the one that killed you.
You don't grow turds in nike boxes, and you intend to keep it that way for this current iteration.