1) Nero and his crew may not have lived long enough to carry out the plan. 2) They may have lacked the necessary scientific knowledge. 3) Only Spock could fly the ship needed to deliver the red matter. That would mean cooperating with Spock, who Nero blamed for Romulus' destruction. 4) Nero's mental state could have been warped by the destruction of Romulus. 5) Without it, we wouldn't have had the film!
Addendum: Even Spock did not seem to necessarily recognize the method by which they travelled through time via the black hole. Later, when the Narada is being pulled into a red matter black hole, the assumption is that the ship is being destroyed, not sent back through time again. It is safe to assume that time travel via black hole is not reliable, controllable or safe. Of course, according to ST IV, any warp capable ship should be capable of time travel, but maybe the TOS crew just kept that secret to themselves!