Most likely because those whales that had personal experience of danger in those areas have died out. And leaving whales who have no aversions to being in those

Most likely because those whales that had personal experience of danger in those areas have died out. And leaving whales who have no aversions to being in those locations. An analogy is humans who have roughly a century between experiences of major ('or 'World') wars. Once the 'old soldiers' with personal experience of the horrors die away, nobody knows how bad those wars were, and so don't have the proper respect for major wars. Consequently, the whole cycle begins again. My belief is that we're not very far away from the next 'Big One'.