Malkut stands at the border where one world ends and the next begins.
In Pardes Rimmonim 2:7:11-12, Cordovero describes the chain of worlds as a series of thresholds. Malkut is the end of Atzilut, the world of emanation, and the beginning of Beriah, the world of creation. What is last above becomes first below.
This is how divine order descends without breaking. Each world receives from the one above it as an effect receives from its cause. Atzilut touches Beriah. Beriah touches Yetzirah. Yetzirah touches Asiyah. The passage downward is hidden from ordinary sight, but the structure is precise.
The boundary is therefore not a wall. It is a seam of relation, the place where what is too high to grasp becomes low enough to begin creation. Malkut receives as an ending and gives as a beginning. This keeps the worlds distinct without cutting them off from one another.
Malkut is therefore not an afterthought at the bottom of the system. It is the hinge. It gathers the fullness of one realm and hands it to the next, so that divine abundance can cross from hiddenness into created life.