Some of this is technical issues. Many old movies were shot in "technicolor" a process that locked in each primary color on its own separate negative. This allowed for just amazing, though not necessarily accurate, color. later color film had its own issues both positive and negative. Today many use digital cameras which struggle to represent the warmer tones accurately. Long wavelengths require a lot of power which has to be stored against peaking/clipping issues at different points in the circuit. This its easier to let it look "cool" or to fudge it into a sort of sepia color scheme that doesn't carry the full range ... I'm butchering this but you get the point that you have to work hard to get digital to look like technicolor!

Worse yet many do the faded look because it's "in the past", which is fine for some interpretations but in general it takes much of the immediacy out of a story. It's hard to ramp up the excitement when the photography hints that it's all over and in the past.