You are correct they CAN serve active duty, but I think you at least understand that an "option" is hardly an "obligation"...
"Little Billy has an active duty obligation.... unless of course.... he doesn't."
This comes down do how "military" reserves are. Yes, they are military. But reservists can run for office, participate in political activities, etc etc etc. They aren't always subject to UCMJ.
It's a weird status, to me at least. And of course, there are benefits to this status. They can be more politically active, and they can do things active duty troops can't. There are also draw backs.... constant healthcare, training, exchange/commissary rights.... and now something like this.
A guy in a class I'm in is a USMC reservists... they aren't drilling.
So here you have a school full of Navy reservists who can't "drill".... and aren't deployed....
This doesn't mean there isn't a case to be made about why USMMA SHOULD be running, but the "they're military" isn't one of them. USMMA is a service academy, not a military academy. That's not a shot at them. It doesn't make them less of a school... it just means the "military academies shouldn't be closed" is hard to extend to USMMA... which isn't a military academy.