The 2 indentations at the "top" are a recognized way to strongly/truly secure blades to handles.
I question that perhaps these "figurines" were trials by apprentice blade makers. The 2 indentations often caused the piece to crack, thus they were made first before the painstaking blade work was done.
If their main craft was making tools out of flints, they were highly skilled at doing so and they gathered lots of the raw materials together, then it would be natural to turn to those materials as a first choice when making art works. Even though they may not have been the best or only choice.
It is also possible that when shapes a little like human forms seemed to emerge by accident from the flint cores they were working with, they saw that as fated and enhanced it.