i just did a simple calculation, about 35k bitcoins are traded on GDAX every day. At its current price of $6900 and a trading fee of 0.3%, the exchange puts about $700,000 in its pocket EACH DAY and it is ONLY for bitcoin. After including all other cryptos, this number can go up to more than $2MM. Since the exchange is active 365 days a year, the exchange's annual revenue can reach almost $1bn!!
you are thinking in us dollar not social support,
this is actually what also drives down the bitcoin price systematically because the exchanges have communal roots, so they "sell" their coins for communal currencies.
additionally there are more and more exchanges comming up