It is not just the FAA that has a say in the dash 7 and dash 10 certification. I expect both Transport Canada and EASA were expecting these airplanes to meet the higher standards within the specified timelines. After the initial MAX certification fiasco the FAA is very cognizant of their breach of trust with other regulators who took the FAA stamp of approval at face value.
Congress can force the FAA to give Boeing a pass but they can’t demand the same of other countries regulators. A MAX variant that could only fly in US airspace would not be of much value to airlines.