It surprises me, though it really should not, that you guys just cannot recognize the flaw in your thinking. You claim that the existing law is not being enforce therefore it makes sense to have a new, nearly duplicate law.
If existing laws are not being enforced then what difference does it make if you have one, or a dozen new identical laws? Since you are struggling with the concept I will answer for you. It makes no difference.
If it makes no difference then why are they doing this? My guess would be that they are playing a game of gotcha to generate selective outrage. If so, Mission Accomplished.
Now as to whether the existing law is being enforced. How are you sure it is not? https://www.ice.gov/news/releases/ice-arrests-275-noncitizens-sex-offense-convictions-during-nation-wide-law