I think Erdogan is under a lot of stress after the attempt coup. Kurds and ISIS and other non Islamic parties conspire against him, and his hands are probably not clean either. He could have turned into the US in search for aid and support, but found no love with Obama who is on its way out anyway. So Erdogan turned to Putin who was more than happy to extend his influence over Turkey. After all, Russia wanted to extend its influence on Turkey since the times of Empress Catherine. Putin is extraordinarily effective.