I have no idea why these two are different. How about making their categories the same, for example, "Science".
If there were to be a rearrangement of categories, perhaps an Education category would be appropriately added to the mix.
It certainly does not make a ton of sense for the two to be in separate categories. However, if you consider a hypothetical third site, "English Teachers", then it seems fairly clear that Professional would make more sense for sites focused at educators, who are, after all, coming to the SE network to grow within their profession.