The reason this doesn't profit is because the spread tends not to exceed the difference in exchange fees. So while there may be a $1 spread between two exchange

The reason this doesn't profit is because the spread tends not to exceed the difference in exchange fees. So while there may be a $1 spread between two exchanges, the sum total of two 0.5% exchange fees on a $1000 coin will only net the exchange profits in fees, and you might earn a penny.