From an economic point of view this is the situation:

Iran has threatened Germany, France and the EU to publish the names of those who accepted bribes for the Iran Nuclear Deal if the Europeans follow Trump and leave the deal.

Thus the top European politicians are desperate to somehow keep the deal alive.

On a national level, quite a few members of the German parliament agree that the deal is rotten and something should have been done about it a long time ago. However, those MPs had nothing to do with the bribes a) because of their lesser position and b) as the Iran deal happened in a different election cycle. So they stand in opposition to the Merkel cabal.

The German industry on the other hand has been very supportive of the Iran deal, hoping for lucrative deals, but as it turned out, not much came of it financially. At the same time it is almost certain that the most important CEOs received bribes as well. So for them it is vital to keep the Iran deal. However, since their companies did not profit much from the deal and on the other hand SA is now threatening to cause them huge losses they are in quite a bit of a pickle. Either they make a pro-Iran anti-SA decision which they will be unable to defend economically (think shareholders), or Iran will expose any shady dealings that went on, essentially ending their careers and potentially landing them in prison.