It was moved because Ataturk wanted the capital, to be more reachable by all Turks. There was also the desire for a physical, and by extension, philosophical separation between the old, Ottoman Empire and the new, Turkish republic. Ataturk changed not only the government, but alphabet, clothing (fezes and burkas were outlawed), made the government secular, added last names, woman's sufferage, nationalized and standardized schools, eliminated gender segregation, and added last names.

In addition, Ankara was a center of the revolution and hadn't been occupied by foreign forces.

-source, wife is Turkish.

EDIT: Possibly better sources:

http://www.columbia.edu/~sss31/Turkiye/ata/hayati.html

http://lostislamichistory.com/how-ataturk-made-turkey-secular/ -somewhat critical

http://www.history.com/topics/kemal-ataturk - surprise, no space aliens