Because the Batman comics were still selling well enough that they didn't need to be rebooted. The immediate aftermath of the original CRISIS ON INFINITE EARTHS was a fascinating mess. Instead of a blanket reboot across the line, series and characters were kinda rebooted in a piecemeal fashion, resulting in odd domino effects: If Wonder Woman has been rebooted but Teen Titans hasn't, where did Wonder Girl come from? If Hawkman has been rebooted but Justice League hasn't, what about all those old JLA stories featuring Hawkman? If Clark Kent was no longer Superboy when he was young, what about the Legion of Super-Heroes? On the one hand, the continuity was a mess. On other hand, DC Comics were more interesting than they'd been in years, with lots of great, creative new takes on classic characters and stories. Honestly, it was the post-Crisis years at DC that first convinced me the "continuity" and "canon" were overrated. If tossing "canon" into a blender produced so many good comics, to hell with canon.