In the course of a life dedicated to belles-lettres and, occasionally, to the perplexities of metaphysics, I have glimpsed or foreseen a refutation of time

books like these are belles lettres, literature, for which the audience is, again, usually small and rather specialized

That is surely why it has no regard for belles-lettres.

The term 'fine writing', or belles lettres, is in this sense ambiguous: it denotes a sort of writing which is generally highly regarded, while not necessarily committing you to the opinion that a particular specimen of it is 'good'.