I have no idea why the change… can’t even speculate.
I kind of feel though since Penn and U Chicago are two vastly different schools w completely different vibes and approaches, If this precludes you from applying to Penn- then you truly were not an ED candidate (someone who is sure Penn is their first choice) but rather a regular decision candidate… Thats just my opinion.
Most of the kids I met who applied to both ED chose Penn over U Chicago -as Penn was always their first choice and Chicago was just a back up.