There are many "cupboards" in the Danish language: Borgerskab, venskab, partnerskab, ondskab, vildskab, ægteskab, etc., In much the same way that there are "boats" in the English language: Friendship, citizenship, partnership, championship, membership, etc. The suffix "ship" in English means a state or condition, and I belive the same applies to the Danish "skab".
I wondered the same and thanks for the explanation. I found this wiktionary page where it says what this old suffix -skapiz that represents "state" turned into in different languages. https://en.wiktionary.org/wiki/Reconstruction:Proto-Germanic/-skapiz