Speculations:

Payout to Creditors: One plausible theory is that these BTC were moved as part of the ongoing efforts to repay Mt. Gox creditors. The bankruptcy proceedings have been lengthy and complex, and these movements might signal a step towards resolution.

Market Manipulation: Another theory is that the BTC were moved to take advantage of market conditions. Large movements of Bitcoin can impact the market, causing price fluctuations that could be exploited for profit.

Security Concerns: Some believe that the Bitcoins were moved as a precautionary measure to enhance security. Given the history of hacks and thefts associated with Mt. Gox, this might be an effort to protect the remaining assets.