The Dane was dumped almost a fortnight ago and replaced by Igor Tudor at Tottenham.
"As management, we continuously evaluate our performance and results. We made the decision after the fight against Newcastle," Lange said"
"We wanted to give Thomas every opportunity to succeed, but in the end it is also our responsibility to act.
"Over a period, performance was reflected in the results - which is why we reached that conclusion."
Tottenham has hired Tudor to the end of the season.
Meanwhile, Lange says their next long-term manager will need to play an entertaining style of football.
"It is clearly something that is very high on the list. We are very ambitious in creating a team that can play dominant football and control the matches with the ball.
"As a club, we have a rich story with some of the world's best offensive players and a very special style of play, which is in line with history and fans."