Big jumps do not happen in the regions that have no special countries. In DV-13 only EU and AF had big jumps. Obviously, the reason is that when regional cutoff exceeds the limit for non-regulated special county (in EU Ukraine is not regulated by cutoff, in AF Ghana is not regulated; Ukraine had a limit of 14682 in EU in DV-13, Ghana - 30538), big jump occurs. The idea is KCC wants to make the number of visas issued per month from any region to be more or less smooth. That is why a non-regulated special country holds the pace, until this country is exhausted in terms of new numbers.
I am not sure about African special countries, but EU special countries both have a limit of about 20000