Don't know about any "official" reason, but Hobie is always trying to make their boats more idiot and accident proof.
Many users put their boat on its side, insert the cart and then roll the boat upright. Every once in awhile someone rolls their boat onto the wheels without the cart being fully inserted. If a side load is placed on the cart without the legs extending all the way through the hull, this can crack the thin scupper walls and ruin the boat. This can also happen if a boat is partially lifted off the wheels in the water, then accidentally dropped back onto the water before the cart fully disengages.
The reinforcements serve to protect the scuppers from these type of mishaps.