Because you can't leave the wall up.
You have to cut it into squares and re-assemble it with additional bricks added to accomplish the new floor to floor height/s.
To do this will be INSANELY costly.
They need to do it anyway.
I am saying a facadectomy where the podium floors use 2 floors of the old building for each 1 podium floor. This would be more costly but when you quadruple the height it would also be much more profitable in the long run.