Well, there's two sides to why that is.

Firstly, to the victors go the history books and the way German culture shifted after the war nobody was going to say anything nice about the Axis with the exception of a few right wing parties.

The main problem is though, the Allied war crimes are less numerous and some easier to justify in war.

Off the top of my head the main one is the rapes as the Allies stormed Germany. Dresden and Tokyo could be argued as war crimes, both had arguable tactical validity based on the cities expected industrial output. Hiroshima and Nagasaki are a tad more dubious but I feel there's a argument that it was justified based on the American's experience in Okinawa. (There's a fantastic, albeit heartbreaking, account from a civilians point of view in Japan at War: An Oral History.)

Meanwhile, we can skip the death camps entirely and Nazi Germany still has major crimes. Their treatment of dissidents. Their treatment of Slavic peoples. Or how they dealt with their former allies.

Meanwhile, the only thing that makes Germany seem cute and cuddily was what the Japanese did in the Pacific. It is a laundry list of needless brutality inflicted on PoWs and Civilians. The Allies weren't saints, but it's hard to color the actions of Japan and Germany as anything but some form of evil.