Lack of commitment is the reason that came to mind. Making them hold sessions during one week, in the same place - Brussels -, instead of week end marathons here and there, is an adequate display of the everyday business of negotiations between sovereign, yet hardly independent, countries.

I just cannot see how government heads would let go any of its powers to someone else of its own nationality. Can you?
One week for europe and three for strictly your own country seems a good compromise. you don't realise the full magnitude of this change.
... Actually, I think the EU is already much more than what we are taken to realise.

(what follows may be off topic. I just assume that you have federalism in mind)
I've nothing against federalism, except that is a higher concentration of power. I distrust large countries. They are prone to destructive policies, home and abroad.
May be a european federation is better. Let's make different errors, better errors, said Samuel Beckett.
At the national level, I've nothing to lose. However, I've the EU to lose. I remember Jacques Delors - "the european community is a slow animal, better that it goes in the right direction".
In fact, federalism is the only subject which makes me feel pleasant about mortality: cannot imagine the ability to decide for futures generations on this subject.