Carl Icahn, one of Wall Street's most prominent and respected investors, has announced that his $7 billion hedge fund will give clients their money back in April. Why? Icahn has essentially lost his appetite for managing other people's money in a mercurial market and volatile geopolitical environment. Icahn will return roughly $1.8 billion but continue to manage his own money.

"Given the rapid market run-up over the past 2 years and our ongoing concerns about the economic outlook, and recent political tensions in the Middle East, I do not wish to be responsible to limited partners through another possible market crisis," Icahn wrote in a letter to clients.

Icahn, Reuters points out, follows in the footsteps of other investors who've decided to return their clients' money. In August, the George Soros protege and hedge-fund celebrity Stanley Druckenmiller shuttered his firm and created a family office for his personal instead, claiming that the stress of maintaining his high performance while overseeing a vast amount of money had grown overwhelming. In February, Chris Shumway similarly announced that he would return all client capital but continue managing money for himself and his employees.

What explains the trend? Icahn cites the unpredictable economy and, indeed, the market has struggled in recent weeks as uprisings in the Middle East have sent oil prices rising and threatened economic recovery. Icahn may be worried that investors will flee his fund in the event of another market downturn, like they did during the 2008 financial crisis, adds Aaron Elstein at Crain's New York Business. But when Drunkenmiller called it quits, he argued that his decision wasn't based on the sour market, telling BusinessWeek “I’ve been through difficult markets before."

CNBC's David Faber has a more technical explanation. Under new rules set to take effect in July, he notes, a hedge fund that only oversees its manager's personal assets won't be required to register with the Securities and Exchange Commission and submit to the agency's transparency requirements and restrictions. "Is it any wonder the Icahn, like Stanley Druckenmiller before him, is making his firm a family office?" Faber asks.