The state wants its citizens to increasingly take care of their own security in old age. And a major factor against poverty in old age is property ownership. So the state wants to increase the ownership rate. To make things a little easier for families with many children, the Baukindergeld was created.
Let’s imagine 10 good friends each with a little house. A builds a house and sells his to B. B sells his to C, who sells his to D,.... In the end, 1 new house was built, but Baukindergeld was paid out 10 times.
Of course. Maximum resource usage. But everyone in the chain has potentially improved their security for old age. And compared to the support the state otherwise provides in old age, Baukindergeld is peanuts. And the condition of sole ownership prevents the disproportionate accumulation of wealth by a few.