Do they not have the full story?
They're all one shots based on 'what if' of pre-exsisting manga's. Some chapters mention which maga they drew inspiration from/ it's based off of exp: http://www.mangago.zone/read-manga/though_i_may_be_a_villainess_i_ll_show_you_i_can_obtain_happiness/uu/mpn_chapter-2095131/pg-33/
Ah this is cute