NEW YORK (CNN/Money) - Japan's stock market got crushed Thursday and commentators were grasping for reasons for why.

It was worries over exporters, it was worry over the banks, it was a reaction to U.S. losses overnight, it was a report of a bribery scandal involving ruling Liberal Democratic Party Officials, it was early word that Sony would disappoint.

It was bad, certainly -- the Nikkei's 5.1 percent slide was its worst drop since the aftermath of Sept. 11 -- so bad that none of the reasons people cited for the decline seems quite right. Though they all may have acted as catalysts for the selloff, the depth of the plunge looks like something else was at work. It looks like hedge funds getting out.

In the week ended Oct. 10 alone (the last one we have the numbers on), overseas investors bought over $4 billion worth of Japanese equities. From late April, when the Nikkei started rallying, foreigners have bought nearly $60 billion worth of Japanese stocks. Some of that cash no doubt came from slow-moving institutional players tweaking regional allocation positions, but much of it was hedge fund players looking for a quick buck. What's known as "hot money."

How'd the hot money get there? Back in April it was clear to many investors that Tokyo's selloff was overdone. Moreover, with Japan's market heavily weighted toward cyclical stocks, it was a great way to play mounting hopes for a global economic recovery.

But what really got the hot money excited, especially as the rally wore on, was the way Japanese authorities kept intervening to keep the yen weak. That meant the yen was unnaturally depressed, and that if Japan ever allowed the yen to strengthen, the value of your Japanese stock portfolio would rise in dollar terms.

As the United States poured on the rhetoric, enthusiasm for Japanese and other Asian issues increased -- particularly as we headed into last weekend's meeting of the Asia-Pacific Economic Cooperation group, where President Bush had promised to take Asian countries to task for their currency policies.

YOUR E-MAIL ALERTS Nikkei Bid and Ask Written by: Justin Lahart or Create your own Manage alerts | What is this?

But Bush appears to have come up cold in meetings with both Japanese Prime Minister Junichiro Koizumi and Chinese President Hu Jintao, both of whom he had asked to free up their nations' currencies. In Australia on Thursday the White House communications director is saying that the administration never thought that currency issues would be solved "overnight."

In other words, the opportunity to make a quick buck on a decline in the buck isn't there any more. And so the hot money is getting out in a hurry.