Since different exchanges are from different countries, the supply and demand price is based on that country. Thats why they are premium priced. People usually exchange within their currency. For example the price of Bitcoin is $18000 in India when its $15000 in Bitfinex. If you send BTC from Bitfinex to Koinex (India) You can convert the BTC only to fiat (INR). That is you have only BTC/INR, ETH/INR, BCH/INR Now if you try to buy some other coin with the INR you got form the BTC, it will also be higher priced like BTC. So you won't be making any profit sending it back and forth.
Also since more and more exchanges are bound to KYC compliance from their own country it will be another roadblock.