I read speculation about why the Sumerians used base 12. It is the highest number that can be easily counted on one hand. Touch your thumb to each finger tip (4). Then touch your thumb to each of your first finger joints (4 more). Then touch your thumb to each of your second finger joints (4 more). 12 total!
For ancient merchants and traders, maybe base 12 made some sense. For example, with base 10, you can divide 10 evenly into 1, 2, 5, and 10 parts - so that's one tenth, one fifth, one half, and one whole. If you work in base 12, you can divide evenly into 1, 2, 3, 4, 6, and 12, so that's one twelfth, one sixth, one quarter, one third, one half, and one whole. So base 12 makes sense if you're in a business that requires divvying things up.