Say you have an adult son who might already be in Canada. The visa officer wouldn't have that information at their disposal.
The purposeful definition of a family member works for IRPA. If the purpose is truly to sanction individuals who might be benefiting from a regime or unscrupulous practices, then that individual should be named, and those family members who are associated shouldn't be painted with that same brush. I think there are charter implications with that.
More than that, you're risking the person's potentially getting into Canada because these officers couldn't possibly know all the family relations of a sanctioned individual unless they're named.