That does remind me. Why are the two cherubim (depicted here as resembling traditional angels) often depicted as kneeling?

There’s really nothing in the Bible which talks about it:
And you shall make a
kapporet of pure gold: two cubits and a half its length, and a cubit and a half its breadth; and you shall make two cherubim of gold, of beaten work you shall make them at the two ends of the
kapporet; and make one cherub at the end on this side, and one cherub at the end on that; from the
kapporet you shall make the cherubs on its two ends. And the cherubim shall stretch out their wings above,
overshadowing the
kapporet with their wings, and their faces a man to his brother - towards the
kapporet the faces of the cherubim shall be.
-Exodus 25:17-20
It only talks about how the cherubim are to (1) be at the “two ends” of the
kapporet, (2) spread their wings and screen it, (3) face each other, with faces towards the
kapporet (incidentally, I know of a few which pieces of art has these
standing).