From a Protestant perspective why didn't the Apostles address the problem of deutrocanonical books? The Apostles interacted with Hellenistic Jews (Acts 17:11) who we know historicaly held deutrocanonical books as scripture, why wouldn't St. Paul or any of the other Apostles make it clear that the deutrocanonical books are not inspired?

It would make sense if the Church is to practice sola scriptura (66 books) upon the departure of the apostles.
The church did not practice "66 book sola scriptura" on the deaths of the original apostles. The biblical canon was not established definitively until the 5th century. It would not therefore have been feasible for the 1st century apostles to state the boundaries of the canon. (Or at least, history would have been very different from what it actually was had they done so).