Say you had a federal election with this sort of result. What is the most likely coalition?
Coalitions that are at least feasible:
CDU-SPD - 46% in this poll, in the area where they may just about reach a majority. Very narrow majority if so and it really could kill the SPD this time.
CDU-SPD-Green - Comfortable majority, probably spells trouble for at least one participant.
CDU-SPD-FDP - Reasonably comfortable majority, but would be bad for SPD and potentially the FDP.
CDU-Green-FDP - Narrow majority, the only option if the SPD were determined to go into opposition but would likely see the Greens pummelled (and the AFD the only right wing alternative…).
Nothing else is feasible, the AFD strength makes it difficult for some of the above to have a majority (nevermind the old 1 major + 1 minor party coalition) while Die Linke falling out would make it a bit easier (and it’s not like any left majority that could even theoretically be included in is anywhere near a majority).