That's because chemistry papers can only be appreciated by a trained chemist, whereas literature is a popular art form which ought to be appreciatable by anybody. Or any educated person, if you want to dismiss the tastes of the great unwashed (it's interesting how literature is one of the few fields where it's still socially acceptable to be a snob).
Now, maybe the Nobel Prize Committee is doing us a great service by uncovering the works of these great authors whose work has never been appreciated before. But in that case, you'd expect them to become popular after their prizes, and everyone would be going "boy, I sure am glad that the Nobel Prize Committee brought Derek Walcott to my attention or else I'd never have read Omeros". But nope, most of the laureates continue to languish in relative obscurity even after they win the prizes.