It seems to be in large part traditional that German parties have formed formal coalitions to support governments - in the Swiss parliament you have "Fraktionen

It seems to be in large part traditional that German parties have formed formal coalitions to support governments - in the Swiss parliament you have "Fraktionen", which can have members from several parties, but are not as formally organized (German coalition governments are usually based on a written contract). Another big factor seems to be that the German Bundeskanzler has the sole power to decide policy and choose his ministers, so having parties form a solid majority to elect and support him is very important. In Switzerland, the government consists of the seven Bundesräte, who are peers and elected independently by the parliament. They rotate at being the Bundespräsident (formal head of government), who does not have special powers.