And the catalyst also stated it was unsure what to do now that one person finally rocked up to its hiding place. It then goes on to note it is incapable of change with out intervention. So it is quite limited in its own abilities. Not to mention that this conclusion it has been operating on for eons is based solely on one set of data when it was first made. So how the hell could it know that peace doesn't last? If anything peace doesn't last BECAUSE the catalyst sends in the reapers to kill them.