Failure of European diplomacy against Turkey

Question by Jean-François Jacob in the European Parliament:

On Sunday 29 November 2015, the Europeans capitulated before Turkey by giving three billion euros to Ankara in exchange for a expected limitation of illegal emigration from Turkey to Europe. This decision proves that a political and identity crisis in the European Union is only "the response of the portfolio".

Indeed, the only clandestine migrants who could have legitimacy – if not legal – to move to Europe would be the Syrians, and that is precisely the ones that Turkey would undertake to manage at our expense within its borders. The millions of economic migrants from Africa, Central Asia and the Indian subcontinent are therefore not affected by this agreement.

Not everything can be bought: neither security nor especially courage. Because the reality is that the EU was in a position of strength, having the option of sealing its border with Turkey hermetically, and then negotiating the aid that we could bring to it under various conditions; The first of these was to demand the complete closure of the southern border of Turkey, through which human and material support to the Islamic State passes.
Why has European diplomacy not acted in this direction?