Most swedes don't want so many kids.
Some people really like to raise children, multiples.
But lets not forget that children are work. More children, more work. The thought that you are 'retiring' and relaxing just isn't so: for 14+ years, you always have a diaper to change, you always need to keep a childproof house, you always need to toilet train someone. For some years, you always have a preteen to watch over. Someone just going off to college. Etc.
But again, this isn't the norm. Even large families rarely have so many children. The amount of folks that try to have 12 children is such a small portion that it isn't worth worrying about and honestly, just parrots right-wing fears that folks are having children to get money from the government.