Why hasn't this storyline been used for a Superman trilogy or better? It was out-selling X-Men at one point, so it wasn't a uniquely Superman reader story. There's enough content to easily fill three films, and enough characters to keep it moving, along with a challenge that's a job for Superman.
80 years of storytelling and Superman films have yet to scratch the surface of quality tales that could be used on the silver screen. This would be a good start.
It even showed off just how powerful Superman really is, as in the end when he became a Cosmic Being to stop Imperiex prime!