Because the traders in both platform are different. The price increases/decreases because of the traders like us. We are placing buy orders and some other people are placing sell order and vice-versa. That's why a little fluctuations between different exchange is possible. But the spread will not be high. If it happens, people will have the opportunity to have arbitrage on two different exchanges.
than you for you great explication
thank you, ALL, for you great explication.
[moderator's note: consecutive posts merged]