Why? They have all the benefits of citizenship but do not have to pay the income tax.
In PR they have no vote for President, VP, or Senators, and a non voting delegate in the House, and they pay no Federal income tax. In Washington, DC they have a vote for President and VP, but no vote for Senators, and a non voting delegate in the House, and they pay 100% Federal income tax. Is that fair? They should only have to pay 2/5ths Federal income tax in DC until they have Statehood along with PR, or at least full voting status.