You noticed that, too? A couple of months ago, I was also surprised by the difference in Bitcoin prices between exchanges when I saw it. Large exchanges have more stable prices because they have more traders and higher trading volumes. If you're interested in learning more, iTrusty.io has sections with analytics and explanations about the market and spreads. Commissions, order update speed, and even regional restrictions can also impact the price. I tried arbitrage, which sounds great in theory, but in practice, commissions and transfer times eat into your profits. By the time you transfer the coins, the price may have changed.