Yet the Eagles were not prescribed from fighting in the final battle, nor from acting as a taxi service from Mt. Doom. 
Right and the Wizards were actually charged to interfere, but not too much. Apparently the Prime Directive from the Valar was even more vague than the one Kirk regularly disregarded. 
It did not need to make complete sense or we would have to admit that the Valar were terrible screw-ups that did not bother to collect miserable traitors like Sauron at the end of the 1st age. Eonwë sent him on his way with orders to appear in court basically. They gave Melkor himself far too many chances and were always afraid to act. They largely abandoned the Avari and Men to Morgoth’s untender non-mercies throughout most of the first age.