Well that could be one possible reason on why they allocate their resources into several accounts for security reasons or because they have multiple large transactions. I mean, if I were to own significant amounts of BTCs, I will never be too sure in which wallet I should store them (definitely a physical wallet!).
Another reason could also be a manipulation or control in the market as movements of large amounts of bitcoin tend to startle the market and cause effects on its price. At the end of the day, whales would do anything that would gain more BTCs at their end.