Because the drafters knew they wouldn't/couldn't/aren't allowed to/would only be able to do so to someone more under the thumb of the US government?
The actual purpose of a law or system is the actual outcome of it and not what it's dressed up to say its purpose is. A law that says "we don't allow mosques unless they're owned by people not descended from countries on a terrorism watch list" is still an infringement of the freedom of religion. We don't have to pretend there's good faith here.
