I think we can blame the internet for that. Before, time created a huge gulf between each stylistic period as they receded into the past. It was very difficult for someone in the 70's to experience much at all of 50's culture except through the nostalgic ramblings of old folks (which idealized these times heavily).
Now the net has created for us a "long now" where cultural elements are basically assimilated and never forgotten (to emerge later as idealized nostalgia). I think its the fist little nibble of the singularity at our heels.
Perhaps, or perhaps it's just a return to a more normal pace of cultural evolution after the rather unusual 1940-1990 period where an awful lot of stuff changed rapidly.
After all, I can't see much difference between the fashion and culture of 1910 and 1890, though perhaps they'd seem larger to someone living through them.
Now the net has created for us a "long now" where cultural elements are basically assimilated and never forgotten (to emerge later as idealized nostalgia). I think its the fist little nibble of the singularity at our heels.