They lost banking access for US Dollar transfers. With dollars trapped within their exchange, the only way people holding those dollars could retrieve their funds was by buying bitcoins with them and then sending the bitcoins to another exchange. But people would only sell their bitcoins for dollars at a premium if they couldn't do anything with the dollars, so the price rose artificially within Bitfinex compared to the rest of the market. People are basically gambling over whether those dollars will ever be retrievable and if so, when?
That is the magic question that we all need the answer to. I have been asking the same question over and over and all the answers I get are "it will not be like MtGox", "Bitfinex is solvent". The people in the forum are either not that intelligent or they are trying to avoid the real problem.