Why did Turkey move its capital to Ankara in 1923?

To break with the Ottoman past. Istanbul was the imperial city, the seat of the sultanate and the caliphate, and it had been under Allied occupation after the First World War - so the new republic put its capital in an inland Anatolian town of about 25,000 people, which was defensible, central, and carried none of the imperial associations Ataturk was dismantling.

The break was the whole programme rather than a gesture. Within a few years the sultanate and the caliphate were abolished, the Arabic script replaced with a Latin alphabet almost overnight, religious courts closed, the fez banned, the weekend moved, and surnames made compulsory - Ataturk means father of the Turks, and it was awarded to him by parliament under the law he had introduced.

The alphabet change is the one with the deepest consequences. It was done in a matter of months in 1928, with Ataturk personally touring the country with a blackboard, and it made the entire previous literature of the country unreadable to anyone educated afterwards. That was partly the intention - it cut the new republic off from the Ottoman archive and from the Arabic-writing Islamic world at a stroke, which is a very large thing to do to a national memory on purpose.