It's better this way, actually -- by allowing such content to be publicly available, law enforcement can easily track down and supervise individuals suspect of paedophilia, thereby better preventing child abuse and keeping them the fuck away from my children.
If you were to go to extreme lengths to make CP completely unavailable on the Internet, then the concerned sick fucks would just resort to darknets or (at worse) encrypted sneakernets, making it difficult for the police to find them.