Interesting discussion, Zip-It's been decades since the last time I read The Stand, and a few years years since I read both Krakauer's Into Thin Air or Into the Wild (which my good buddy who also teaches AP English Language and Composition teaches). The Stand and other Stephen King was my guilty pleasure in high school. I don't recall being annoyed by the vocabulary in any of them, but as I said, it's been quite a few years.
I don't get to read nearly as much book-length contemporary fiction or non-fiction as I would like because my teaching focus is more on essays, long-form investigative journalism and cultural commentary that I can revolve around a more traditional anchor novel like Dickens' A Tale of Two Cities or Steinbeck's The Grapes of Wrath, both of which contain some obscure words, especially Dickens. So you have probably just read much more contemporary stuff than I have to notice this trend.
Do writers from many eras including our own often show off their fancy 10-dollar words that no one will ever use? Absolutely. But another disturbing trend that I am noticing is that even our smartest students in Honors and AP English classes in some cases have shockingly limited vocabulary, probably because they just don't read unless its' assigned by a teacher, and even then there's always Spark Notes (which, don't even get me started!).
Here's another interesting exercise that's kinda related (though I know you're mostly talking about fiction). Take a stack of news magazines from the 50's and 60's, and one from this time period, and compare the writing. It's almost like two different languages. Certainly the vocabulary and lexile levels have been simplified for an audience that would generally rather be titillated and entertained than challenged.
I'll keep an eye out for the trend you're describing.