it is simple, just look at a map, russian army can not leave black sea without going to turkey, from turkey, you can reach easy for russia or the middle east. It is simple, they are in a good strategic position. Turkey is the american Cuba.
@TheDivineInfidel it is simple Turkey does have a nemesis: Kurds. Kurds are fighting against ISIS, and ISIS is fighting the Kurds. So, if Turkey would attack ISIS, the Kurds would have fewer enemies to deal with.
In the turkish perspective it is way better for them to let ISIS fight against the Kurds, so they don´t have to do it anymore.
And not only this, Turkey can use the war on ISIS to fight against the Kurds without having problems, so better put some oil into the fire, because if this conflict is going on, they can fight the Kurds even longer.