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!!
This is very surprising and yes the crazy too because this calculation is far away from my expectations that how can a exchange earns such a lot from a single cryptocurrency naming bitcoin, though BTC is very successful and sustainable cryptocurrency but still an exchange earning such a huge amount in a year is really surprising.