Tottenham's modest January window drew criticism, including from captain Cristian Romero.
Lange told Sky Sports: "I personally believe the new European format changed the dynamic a little.
"You are playing two very competitive matches (in January), with the fact that not only us but a lot of teams have what they would say is too many injuries.
"(That) meant that in January very few players who could make a difference for us now or in the future was available and then it's back to the point even though the squad is too short, we still have players we are unable to register for the (Champions League) last 16.
"So, to bring in players that cannot help us now or we don't believe have potential for the future, that unfortunately for me doesn't make sense."
On Romero, Lange also said: "Romero is here, he is our captain, he is here on a long-term contract with the club.
"I think we have been clear as a club that we have dealt with that internally and now it is about being together."