Next week's tournament is the first of the European Tour's three Final Series events and four-time major winner McIlroy was to be the star attraction.
A recent rocket attack in the Antalya region, which hosts the event, led to the Northern Irishman's withdrawal.
"It was weighing on my mind and I slept a lot better knowing that I'd made a decision," McIlroy, 27, told AFP.
"I  gave it a lot of thought, basically all week.
"The fact that I have won the FedEx Cup this year and that I have won the Race to Dubai before made the decision a little bit easier."
McIlroy will move up to number two when the latest world rankings are published on Monday, as a result of finishing fourth in the WGC-HSBC Champions in China on Sunday.
He had spoken of his desire to win at least one of his last three events this season - in Shanghai, Turkey and Dubai - to try to win the Race to Dubai for a third year in succession.
McIlroy, who is more than a million points behind leader Danny Willett of England, was set to have top billing at the Regnum Carya Golf and Spa Resort in Antalya on Thursday.
Tiger Woods had earlier pulled out, the American 14-time major winner saying he needed more time to work on his game after a long injury lay-off.
McIlroy's withdrawal leaves Masters champion Willett as the top-ranked player in the event.
Earlier this month, European Tour officials investigated reports that the southern Turkish holiday resort region of Antalya was hit in a rocket attack.
Turkish media reported that two rockets were fired from a mountainous area close to the highway linking the city of Antalya with the resort town of Kemer.
No-one was killed or injured in the attack, which hit a fishing company's storage house and open ground nearby.
It is understood the Tour received assurances from security experts that it was safe to stage the event, won last year by Frenchman Victor Dubuisson.
World number three Rory McIlroy has withdrawn from the Turkish Airlines Open because of concerns over security.