Why war dominates naval-history publishing

Why are there comparatively few books on long-nineteenth-century naval and maritime history?

Because wars are easier to sell, publishers steer authors toward conflict-centered subjects and structures.

The question notes that the long nineteenth century has fewer naval and maritime studies than the twentieth. The blunt answer is that wars sell books. A publisher's advice to structure a book around a world war illustrates the same commercial pressure. The shape of the historical literature can reflect market expectations as much as the richness of the surviving subject matter.