In my opinion, the answer lies in the functioning of the political institutions at the present stage of integration. All major decisions are made by 17 sovereign democracies. Unlike a unitary state, the euro area has 17 heads of state or government, 17 ministers of economy and countless national parliamentarians.
Not surprisingly, in complex matters such as European ones, their messages to the media often diverge. As we have seen many times, these differences can lead to echoes and adverse interactions between politics and markets that ultimately end up undermining the effectiveness of the decisions taken, however important they may be.