MT GOX was the very popular crypto exchange of 2013, You can compare it with todays binance.
But this exchange got hacked and lots of peoples loose there crypto currency in the haking attack, So they decided to give the money back to the peoples and they were selling there huge number of bitcoins from jan to june to give the money of all peoples in there fiat currency.
This was also a reason of bitcoin price dump multiple time. Some one given a idea to mt gox that why are you selling btc to pay your customers in fiat, jut give them btc of there value.
There is a an announcement from MT GOX that they will not sell there remaining huge quantity of bitcoin, so that is a really good news for us now MT GOX will not sell there remaining btc on exchanges.