Sigh do you understand treaties that Germany has sign over 60 years, and not a single treaty but many over a long period of time prevent this each individual subsequent treaty modifies the first.
Furthermore yes the treaties do bind the hands of Germany for it prevents you even starting negotiations without the other members at the table.
-----
But seriously Cannoli are you arguing over the number of angels on a pin.
Are you trying to make a sophist answer on why this is a good idea, or a (in the negative sense) scholasticism answer, regardless the discussion you are trying to make is a senseless and silly one where it is all about will without carrying will the discussion have real world consequences.
Trump trying to sign a trade deal as a negotiation where it is diplomacy but has no economic effects due to treaty or economics policy that end nowhere is ultimately a silly thing for the Treaties prevent it from coming to real world fruition. It is a waste of time, and if Donald Trump need 10 to 11 answers of the word No from a woman ... to get the point. Well what does that say about him and what does that say about you where you want to say he really did have a good reason why he asked 10 instead of 9 times.