Loeb says one reason why he's returning the capital is because of the fund's exceptionally strong performance.
From Third Point's Q3 letter (emphasis ours):
Year-End Return of Investor Capital
Third Point's assets under management are currently $14 billion. Our increased size is primarily a result of a net annualized return since January 1, 2009 of 24% to investors in the flagship Partners fund and 29% in our slightly levered Ultra fund, which have led growth in the capital base since our initial close to new inflows in mid-2011. In an effort to moderate this growth, we have decided to give back a portion of 2013's cumulative profits to investors.
We plan to return approximately 10% of capital in our private funds. This amount will be based on year-end account balances and will include any requested redemptions from investors, the deadline for which is October 31st. The capital return will be made to all applicable investors on a pro rata basis, but will exclude employee investments and the investment from our listed vehicle feeder fund (which will separately pay a redemption funded dividend)
Third Point is up 18% YTD compared while the S&P is up 19.8%.