When that happens, it becomes a natural thing because, considering the several matches they have participated in, the players are sometimes injured and tired, so Real Madrid's performance is reduced. They know that in the Bundesliga the chance to win may be small, so they focus more on their strength in the Champions League and try to get a victory there.
You mentioned the Bundesliga which has nothing to do with real madrid even real madrid has never faced a team from the Bundesliga this season. So take a look at what you're writing.
Indeed, Real Madrid have other hopes after they were unable to compete with Barcelona in Laliga this season, but that is not a good thing for them because they have to improve next season to become a strong team again and win Laliga.
One of Real Madrid's ambitions is the Champions League, which they fight for as best they can, but in the semifinals, Real Madrid will face a team from the EPL, namely Manchester City, which lately Manchester City has performed quite brilliantly in the Champions League.