Even in a garage with flat floorplates, you still need ramps between floors obviously. In the case of a large garage, you can still have most of the floor be flat and suitable for future conversion, but in a compact podium like this there's no way to avoid sloping large portions of the floor area.
I'm guessing they need that solid panel at left for shear, but they may extend the glass screen wall in front of it.
I did find this rendering which may be slightly newer, it looks like the screen wall has switched from glass to a metal mesh and is vertical stripes rather than being a randomized pattern:
https://chicagoarchitecturebiennial....-southbank.jpg