You will notice that the cities of the islands nearby to Turkey are pointing towards the Turkish mainland instead of Greece. That's because they had a very strong relationship with the mainland cities of Turkey (mainly commerce). These particular cities, aside being established by Greeks millennia before, had a very substantial Greek speaking population even in modern times. That is because before 1923 Turkey was still the Ottoman empire, which just like most empires was a multicultural empire. It was only after 1922 that these cities became predominately Turkish due to population exchange.

The fate of the borders was decided by the Treaty of Lausanne (1923).