Books teach abilities and specializations rather than single crafts; many are tiny-supply world drops with some of the most erratic charts in the catalog. This page narrows Recipe down to Book only, so the table stays scoped to one subtype instead of the full category list.
Because this table is filtered to Book only, it stays short even when the parent category is large — a fast way to scan a single subtype without paging through unrelated items.
The "Browse subcategories" links on the parent Recipe page list every other subtype if you want to compare markets side by side.