Why do Kenyan top bar hive walls slope inward toward the floor?

Greetings,
I am new to beekeeping and was looking at the different styles of hive types. I am currently looking at the "Kenyan" top bar style hive and had a question I was hoping someone might be able to answer for me. Why do the sides of the walls slope inward toward the floor of the hive? Why not just have straight up and down (vertical) walls?
Thank you

Firstly there is a type of hive with straigh walls its called the tanzanean top bar hive .
Secondly the reason for the slope is that it matches the natural shape of the comb produced by the bees , ok the bees dont do straight but it comes close and this means that there are less air spaces for the bees to have to keep warm or full of bee scent . So its more efficient and less stressfull for the bees . Thats the idea anyway

David

I have heard the following reasons for the 60 degree slope on the Kenyan:
- less attachment of comb to the side of the hive
- less prone to breaking or slumping due to smaller size of combs