Why didn't Hitler have the arc de triomphe torn down?

Hitler didn't have animosity towards Napoleon--it was too distant in the past. In fact, he visited Napoleon's Tomb when he went to Paris. He appears to have admired Napoleon as someone whose example he could follow. When he visited the tomb, he commented that Napoleon's tomb was arranged wrongly. People look down upon napoleons's sarcophagus from an upper walkway, while Hitler, always the showman, said Napoleon should be on an elevated platform so that all could look up upon his greatness and feel minuscule in comparison.

On the other hand, Hitler, like a lot of Germans an Austrians, HATED the French for what they considered France's humiliating treatment at the German surrender. He therefore engaged in many activities to humiliate the French. He initially did not want to allow them to participate in the 1936 Olympics. He was ultimately dissuaded from that, for the sake of publicity. Later, though, He made them sign their surrender in the SAME train car, at Versailles, where the Germans had surrendered in WWI. Imposed crippling payments on them. He marched German troops down the Champs Élysées and through the Arc de Triomphe--a humiliating defeat at least as bad as destroying the Arc. Hitler wanted to seize France's treasures for the Reich--much better than destroying them. A movie is soon coming out, The Monuments Men, that may cover some of this struggle to pillage France of its treasures. However, once it became clear the Germans were losing Paris, Hitler did give the order to utterly destroy Paris. The Arc de Triomphe, the Louvre, the Eiffel Tower Notre Dame--all would be rubble. General Dietrich Hugo Hermann Von Choltitz defied that order and Paris was saved.

Tl;dr Hitler admired Napoleon, no animosity. But hated 20th century French,aggression aimed at them.