at binance from March, 12 up to now (April, 11) someone bought bitcoin and spent 600 mln usd to keep bitcoin at price from 7,200  up to current 6,800

all people there sell bitcoin, and someone bought all this btc, total cost of purchases are about 600 mln usd 
Delta  between btc that was sold  and was bought - about 100 000 btc

any ideas - who, why?