It is the same thing as google. Here is the answer i cited from Chinese version quora(zhihu).Because it too long ,so i plan to translate it by google translator.

Google is a company, a company of any behavior around the core is the company's goals. Google out of China, therefore, the most fundamental reason for certain is that it did not reach the expected target. Here we make such an assumption: if Google into China after its desired effect, it will leave? I'm afraid, even if let it filter more a few pieces of information are also willing to it. So, the core reason of the Google left China, must have not reached the expected goal. Here to explain what is "not the desired goal:" a lot of friends in all kinds of data to illustrate that how successful Google in mainland China, but the question is: for a company, if it is able to give up a market, the success have not reached a height, a "target". Look at apple: apple mobile phone is compatible with the wapi, soon it is boosting wapi status. Why apple so spineless don't have their own values bow to China?

Do You Know Facebook is Banned in China?

Maybe there are some other factors, however, will you speak a little here: 1) the baidu. Baidu certainly don't want to Google in China, so it may do some things. Have a friend here said I did not what to say. 2) before Google out of China, is China and the United States on the wireless network standard to the most rigid. At that time China has launched a wireless network protocol standards: wapi. Wapi is simply wifi + point-to-point encryption (wifi at that time still no encryption). China says everyone use wapi, safety. But the United States to "make China master information industry standards say are a threat to the global information security" on the grounds that tried to stop the implementation of wapi. Then China settle for second best for "electronic products entering China must support wapi", at that time, Intel immediately objected, and threaten the Chinese said "if the Chinese don't want to put forward such a request, Intel's chips embargo against China". Eventually the Chinese government caved in Enterprise and the dominance of foreign investment(like today's Google in Europe).

China is the only country where facebook is banned? 

I'm not sure about this. I guess there are a few countries too where Facebook has been banned for several reasons. such as Israel, Iraq!

 
WTO in principle does not require member states must immediately open these short board, but the United States urged China must open. China's compromise. China says open open, as long as we can fair competition. But the result? The United States is to kill your wapi, do you have a temper? It can make Chinese very angry. So the Chinese government is bound to return. Today, it seems, response is: don't you play with my hard sell? Good, you also don't want to come China market points to eat the meat. A friend said when trade friction, so there is no obvious evidence of Google and wapi has a direct relationship. For this statement, a master is the first to admit that, a master does not very direct evidence that there is relationship between the two. So you can say a master this is conspiracy theory. But, I'm please to know about the China and the United States since 3 years
Since Google has been thoroughly occupied the market in Europe, European countries was very depressed, no chance to get your engine, so the eu had to three days at both ends with Google monopoly and occasionally sent money or something... This phenomenon also let China to Google, wary.