صوم رمضان صوم فرض، فيشترط التعيين له كالقضاء
Ramadan fasting is obligatory, and so it is argued that it requires designation just as makeup fasting does.
Both fasts are obligatory, but the Hanafi counterargument emphasizes that Ramadan is a legally designated time, while a makeup fast can be performed on other eligible days and requires specification in a different way.
The point is not to ignore the shared status of obligation, but to ask whether it is the decisive cause of the intention rule. The legal role of the appointed time must also be assessed.