Given that Apple silicon is pretty new my guess it porting and testing , I would also add not all ARM chips are exactly the same , there will be some minor nuan

Given that Apple silicon is pretty new my guess it porting and testing , I would also add not all ARM chips are exactly the same , there will be some minor nuances for sure . Perhaps it is also some funding and access to the kits and dev time , updating gcc is not a full time job for most of the contributors after all.