Most of these whales wallets are owned by institutional investors, this type of investors are always using they're funds for huge transactions payment which results to keying down a different investment at the end. The idea of moving funds from one wallet to another is actually not advisable but once a user detects prone in such wallet, the best move is to transfer it out to a different wallet do avoid lost of funds.
One of the possible reasons to move huge amounts of Bitcoins is a security! Is it a breach or whale found a wallet with better security,
nobody can say. There are many possible reasons why someone is moving Bitcoins from one place to another.
I saw some people trade on these movements. They follow exchange addresses and monitor all big incoming or outgoing transactions.
It's interesting for me to read about transactions of huge amounts, and possible reasons for that. I usually see some of that on Twitter,
but I do not trade based on this informations.