A split opposition and a 10% voting threshold. The opposition would essentially have to lay aside their differences and form an anti-Erdogan party. That's unlikely, because the Kemalists and the Kurds hate each other.
The Kemalists want one indivisible Turkey with only Turks. The Kurds not only persist in calling themselves Kurds instead of Turks, but they also want to secede. These two points of view don't play nice with each other.