One reason, clearly, is the swapping of the third-person omniscient narrator who sees and describes everything for us reliably for a host of narrow and fallible little subjectivities, and their limited perception of what there is to see, think, feel.
However, there is too the reality that we live in an age of visual media which has driven home to us just how difficult it is for the written word to compete with the camera as a way of conveying images in all their vibrancy, immediacy, texture, grandeur--leaving many of us less inclined to try, and perhaps with less sense that there is a need to try. (Whatever it is, you've probably seen it on TV before, and so it seems it is enough to evoke that.)
Perhaps more importantly, film and television have accelerated the pace of storytelling, too much so to allow any room for thick description--confronted with which we are apt to get impatient to move on.
And of course, many have made a virtue of describing less (one thinks of the enduring cult of Hemingway), while more generally the trend of recent decades has been toward easier-to-read, less demanding books of smaller words connected together in shorter sentences, compiled together in shorter paragraphs in littler chapters (even as books of doorstop size became more than ever the standards).
Have we lost something precious in all this? Certainly there are those who have put subjectivity, evocativeness, briskness, minimalism, accessibility to good use. Still, at their best there was something to be said for the lusher descriptiveness of the nineteenth century novels. Take, for example, Peter Washington's appraisal of Balzac as
a writer whose delight in appearances encompasses every mode from the interior decorator's passion for glitzy surfaces to the philosopher's interest in the hidden depths behind them . . . He has an extraordinary grasp on the materiality of the world, the sensuous quality of objects. All his books are filled with things . . . [and] Everything has its place in a complete vision of life at a particular time and place.The vividness of his settings, the solidity of the world he imagines and the characters with which he peoples it, would be difficult to imagine without all this, while as Washington also noted, "[t]he dramatic virtues of this method--its distance from mere description--becomes apparent at critical moments in the novel." The details--the difference between a wax and a tallow candle in Eugenie Grandet, for example--are neither decoration, nor mere "symbolism" of the sort on which impressionable middle school students develop neurotic fixations, but the sorts of little things that make up the life he describes.
Novels like Balzac's strike me as more fully novel-like than anything we are likely to encounter today--epic depictions of life, worlds on the page such as Modernist and postmodernist narratives, in their smugly showy fragmentariness, obliqueness and unreliability rarely even try to deliver (and still less often, succeed in doing), no matter how much admiring theorists tell us otherwise. And so while it is well that leaner styles are accepted, the achievements of writers working in that other mode ought not to be slighted.
My Posts on Literature