The SPD is not a great comparison number because as a party it has a severe identity crisis. They sold their soul by being in a big coalition and many people that remember what the SPD stood for donโt find the party it once was. Even worse young voters donโt see themselves represented by them because they see no difference to the opposition. That is why the Green Party has done so well.
The last election the SPD got more votes than everyone imagined and they still are not able to show Germany why they are a better choice.
They only got more votes than imagined because the candidatebof the conservative CDU was so grossly incompetent, he laughed in the background of the president holding a speech mourning the hundreds of casualities from a flood.
The voters that them voted SPD were people whos political mind does not consider more options than CDU and SPD with the CDU being the choice of habit.