I see no more oddness to the fact that many people under 30 don't "get" _film noir_ or many other movies from the thirties and forties such as classic musicals, than most people don't get classic opera. I was lucky to be exposed to Verdi, Frank Sinatra, Charlie Parker, and Dylan before age 13 and acquired a taste for all of these types of music early, but I understand when some people find all of these types of music hard to listen to. The movies from the 30s and 40s and into the 50s were made in a way that "feels" as far away from some of us as 18th and 19th century opera felt far away to the average Beatles fan.
I have to say that I think you are showing a bit of a lack of empathy here. I grew up with these movies on afternoon afterschool television. I had already seen hundreds and hundreds by the time I was sixteen. And like opera I do feel that these movies are an acquired taste. This was made clear to me when I went back to school late in life. Among people under 30, it seems to me, only movie buffs consciously choose to watch these movies. Many react to them in the way my younger sister reacts to John Coltrane and Charlie Parker. What is this? Why are you listening to this? How can you tolerate it.? Where's the tune? Why do the notes get stretched so much? Why are there so many notes?
The reaction to the old films is "Where is the plot? Why is every scene stretched out so much? Who is who and what is what in this movie? What in the world is this camera movement trying to say?" These movie unfold too slowly and yet somehow are able to "signify" shot for shot, camera movement for camera movement, too quickly.
You must become acculturated to such art in order to feel and understand it. Most film noir is murky to say the least. Take a movie such as Tourneur's "Out of the Past." I have shown this movie to half a dozen people of a certain (younger) age and they just don't "get it". It moves both too slow and too fast. The emotional impact of the ending - where the deaf boy honors Bailey by lying about him - often has to be seen twice before the impact is felt. ("The Big Sleep" has to be watched at least 5 times just to figure out that the "plot" has not sollution and wasn't meant to have a sollution.) If out of the past had ended quickly on the car crash then we would have had a sort of Tarantino ending but the film is not meant to stop here.
Take films such as "In a Lonely Place", "The Strange Loves of Martha Ivers", "Sorry Wrong Number", "Criss Cross", "The Lady from Shanghai," or a late comer such as Polankski's "Chinatown". These are all truly strange films and there "slowness" hide the fact that you miss a lot if you don't look closely. Not only that but the camera work in all of these films "signal" in a way that people under thirty are not used to, unless they were exposed to these moview early.
I find that good "entry films" are " Mildred Pierce" and "Double Indemnity". Both of them teach you how to watch them as they go and both give a little education on how to make a studio film in the 1940s.
I could write about screwball comedy in the same way. In the first place many people don't find these films funny. But this is another story.
Jerry