Comment by brazzy

Because the Pirate party is taking away voters from both the traditional conservative camp (FDP, CDU/CSU) and the traditional social democrat/Green camp, yet is too new to be seriously considered as a coalition partner for a government. That means a grand coalition (CDU/CSU and SPD) led by Merkel becomes more likely - the same one as in the previous administration, before the FDP gained enough votes to have a traditional conservative coalition, but the FDP is currently vanishing into obscurity.