I really have no idea how these pleas can appeal to anyone.
I myself am further to the left than the dems, so I vote with them. I find their messaging so spectacularly weak. They are always trying to guilt people into supporting through this narrative of "we are weak and about to get crushed, save us." I find it so off putting, I wish we had other viable parties and could get rid of FPTP so we don't have to constantly select between these two.
The 5% thing is a post-WW2 innovation to prevent a small block who just want to tear everything down from getting into the Bundestag and causing chaos. The AfD did manage to get over the hurdle and stay in the last two elections, but can't get too wild - otherwise, they probably won't make that 5%.