We often get "why isn't X a case" questions, especially for USA.
The problem with most such questions is that they are really two questions in one:
"Why isn't there a law for X"?
Which has one, and only one, generic boring answer of "because there is not enough political support to make X a law by following usual process of establishing a law"
And the second, implied "Why isn't there enough political support to make X a law"
Which is very hard to answer objectively, as you're asking about motivations of a large number of people - which are often unknowable; and definitely usually widely diverse.
I'm not really sure what my thoughts on this are other than such questions seem worth thinking about - should we prohibit them? force them to only ask the first question (and then VTC as duplicate pointing to a canonical answer of how US political system works)?
 some rare ones can also be answered with "because a law for X is unconstitutional - which makes them, if not offtopic explicitly, but a better fit for law.SE