Here is my theory on that burial thing.
The history we know was written by wazungus who came to Kenya in late 1800s.
When they came to Kenya dysentery and small pox followed them ravaging the people. It could be they used biological warfare by intentionally spreading these diseases to weaken the resistance as they worked to colonize the people.
https://www.pilotguides.com/articles/european-conquest-spread-disease-biological-weapon/
So contagious were these foreign diseases that the people (Kikuyu) would leave the infected family members in the woods for fear of spreading the infection to the healthy members of the itora (neighborhood)
So when the wazungu found unburied bodies in the woods they wrote that culturally Kikuyu didn't bury their dead. History is written by the winners, remember?
I don't believe that the Kikuyu didn't bury their dead. Imagine having to drag a dead donkey, dog, cat all the way to the forest when it's easier to either leave it where it is or bury it.