There are many reasons of why whales could do something like this, the most obvious is that they could feel that there was a chance that their private keys were compromised at some point in the past and they decide to move their coins from an address that could be compromised to a new address that doesn't have that problem, as you say it is also possible that they decide to split their coins to different addresses in order to protect themselves in the case a hacker can obtain one of their private keys.

Now it is also possible that they are doing this in order to create excitement over bitcoin because as we know if someone moves such a huge amount of money then that is bound to make the news.