Speaking of popular movies these days being as long as they were back in the mid-century, what about books? When I get more time, I'll go through the top 10 best-selling novels from the Publishers Weekly list that goes back over 100 years.
But for now, consider what's popular with young people -- i.e., those who are supposed to have short attention spans, too restless and fun-loving to want to plow through a long slog of a book. The novels in the Hunger Games trilogy are nearly 400 pages, those in the Twilight series between 500 and 750 pages, and although the earliest Harry Potter books were just over 300 pages in America, the later ones were pushing 700, 800, 900 pages.
Not having been a teenager, nor in the target market anyway (chicks), I have no memory of what the hot young adult novels were in the good old days. So I went to check some lists and comment threads, and there were a fair number under 200 pages, at least back to the '60s classic The Outsiders. Most seemed to be around 200-300 pages. V.C. Andrews' novels that began with Flowers in the Attic was the longest popular series I could find, and they averaged around 400 pages.
Judging from the one-time fans writing about them so many years later, it sounds like these books were a lot more poignant than those of today. The more hard-edged subject matter probably contributed to that, but the shorter length must've also concentrated it to leave a stronger impression on the reader. Teenage girls had better things to be doing in the 1980s than casting themselves adrift in 800 pages of emo moping. Talking to all those boys, for one thing, rather than locking themselves in their rooms all day long.
Maybe it's not too surprising that today's OCD audiences would prefer 700-page teen romance novels. They're the same ones who praise video games that "don't get going until the 30-hour mark," or who could surf their Facebook feed for 6 hours straight every day just liking random comments, more out of compulsion to stay on the treadmill than out of any genuine enjoyment. It's another one of their joyless addictions where quality doesn't matter, as long as there's always a bit more "content" to continue consuming.
How do I know they're not really getting into these books? You rarely see their facial expressions change when they're reading, as they would if the books were truly engaging. The rest of their body doesn't respond either, e.g. by leaning forward "on the edge of their seat". It's more like they're crawling back into the womb, to sleep forever shielded from the frightening real world (where they're already sickeningly pampered). They have that vegetative glaze on their face the entire time, as though the "universe" of the novels had no remarkable features, nor the characters any personality -- anything that would strike an emotional chord in the reader. It's more like a really long episode of channel-surfing, sifting through this, that, or the other pile of dusty junk, and coming up empty.