See that's my take though... "Seems like". I don't know the metrics off hand. Are there hard numbers to back this up? Honest question. And then when you take those modern numbers (say how many films are "reboots/re-makes") and compare them to the 50's, 60's, 70's and 80's is it really all that different? And when we take into account things that are just heavily influence by earlier entertainments of one time or another it gets even hazier. I mean, we can all talk about Star Wars as this beloved cultural force, no pun, but forget that it's a pastiche almost of the serials from the 30's/40's/50's, WWII films, Western folklore and myth and nice sprinkling of Eastern philosophy and mysticism.
I think that a lot of this comes down to the post 60's cultural obsession with "authenticity" and "originality" for what ever reasons, while turning a blind eye to the idea that each successive generations always rehash and reinterpret stories, and that the way Hollywood (and the culture at large, cuz SOMEBODY is choosing to see the TMNT and TRANSFORMER films in greater numbers than say seeing Tome Cruise in EDGE OF TOMORROW) is choosing to go to the well of the past is just the modern incarnation of this phenomenon.