Turkey has already had €3bn from the EU in exchange for cracking down on illegal immigration but they've done pretty much nothing in return. What are they going to do with €6bn? Well, they say they'll take back unregistered illegal immigrants who've made it to Greece and replace them with registered illegal immigrants.
In addition to the €6bn bung, Turkey also wants fast-tracked EU membership, giving it access to eye-watering sums of money and allowing 77m Turks to live and work in EU countries including the UK.