Question: Almost all WWII movies depicts Nazi officers and soldiers as well-dressed and handsome.

On the other hand, allied officers and soldiers are always shown wearing torn uniforms, etc.

Why?

Answer: 
My answer here is to the point of history and not movie making ... Please remember what Hitler was trying to build and exemplify, that of the "master race". His Nazis would have fit that mold to a tee. Blond, blue eyed, blah, blah, blah. You get the picture. This may now be a bit over done in movies, but it is what it is. The dress may very well just be an extension of this. Allied troops overseas would not have the supply chains available to them to keep their uniforms freshly pressed and tidy.
@Paulster2 well you have a point, which is true. The 1st reason is that half of the time these movies are about what they did rather about the war so mostly they were captors of some people or whatever the situation was germans were in much safer locations. The 2nd reason is the color of the uniforms. Allied uniforms were often brown (dark or light brown), but the germans wore black / dark green / olive green uniforms, so the color affects you thinking that brown is less formal than black and dark green. The 3rd reason is that you often see less allies commanding officers than german officers. And pay attention to any other movie, usually the badguys are richer, well funded and the good guys are poor or not well-funded. And this fact applies to the majority but not all, regardless if the fact it's about a war, about mafia, or drug dealers. These plus what our friend said about Hitler's Agenda.