Are all master degrees fully funded for North American universities?
Most master's degrees are not fully funded (or even funded at all) in the United States. Funding varies by of study field. Some fields, such as business, will rarely offer funding, while others are more likely to. 

Perhaps you have been looking at PhD programs in math and science - these do tend to offer funding. But that is the exception, rather than the general rule.  At the master's level, funding is more rare even in these fields.