The real answer is that Geoff Johns and Scott Snyder dislike Catwoman. So Johns came up with something to break up the Batcat thing in Forever Evil and Snyder took advantage of it to push the break up further in Batman Eternal. The Catwoman solo with her as a mob boss who hates Batman was a spin-off of Batman Eternal. after all.
Before that several writers had been shyly setting up Batcat. For example John Layman's Detective Comics. Even Johns' own Justice League of America run had Catwoman as being into Batman, even if he later on wrote her and Steve Trevor fucking or whatever. Still it was basically the two nursing each other after being left by their loved ones.
Honestly, i've no idea what Johns was trying to set up back then with this whole mess.