Why haven't Real Madrid won the league this season?..?

Simple : Because of overconfidence *_*

The Champions League?

Cannot blame Mourinho. Madrid's performance last week was not one of professionals. The players made a mistake which was difficult to overcome. I believe Mourinho when he says the team "knew everything" about Lewandowski. Yet the players allowed him to score four goals on them.

La Liga?

I get the sense that everything is a struggle over there which makes it difficult to coach. It doesn't take much. Squabbles between the players and squabbles between management themselves will likely have a negative impact on team performance. The quality of the players is still there but the focus has been lost.

Jose Mourinho prepared a team that can beat Barcelona... and eventually forgot about other teams... that's the very reason why they were beaten by Dortmund in 2 legs

They did not perform as well as Barcelona did especially at the start of the season.

I think there was tactical error on Mourinho even the fact he has quality players, physical teams of german quality were a surprise too all, i feel this was one factor.

They were not consistent enough and lost some games they should have won. Too much reliance on CR7 if you ask me or maybe the special one is not so special after all