As someone already said, they only want to become a state so the US tax payers will bail them out.
There has been a strong statehood movement in Puerto Rico for more than 50 years. The main argument is based more on security than economics. Most Puerto Ricans would suffer financially under statehood since they would be liable to pay federal taxes. Under the no taxation without representation concept, they are exempt from federal taxes now.
It could be argued that statehood with give them protection under Title 9 of the bankruptcy clause, but Congress could do that alone by law. There is certainly no guarantee that statehood would prompt a bailout. Remember President Ford and NYC?