The Supreme Court doesn't.
It's not like any interpretation is valid but there are plenty of valid ones.
And of course it makes sense, because the legal system was created by the very laws it upholds. If you think it should be different, then you'll have to convince a lot of people to change a lot of laws and probably parts of the US constitution
It does, because the Supreme Court's ruling is the legally binding interpretation.
The EFF are just some people with an non-legally binding opinions.