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Why do continental Pacific islands tend to be larger and have richer soils?

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Map of the Pacific Islands region showing political boundaries, major island groups, and countries such as Papua New Guinea, Fiji, Samoa, French Polynesia, and Kiribati. The map uses color shading to indicate elevation and ocean depth, with key islands and capitals labeled throughout the central and southwestern Pacific Ocean.
Pacific Islands

Continental Pacific islands are generally larger and possess richer soils because of their distinct geological composition and formation compared to oceanic islands.12

Located southwest of the Andesite Line, these islands are continental in character, meaning their structures are similar to the coastal mountain ranges of adjacent continents. They are formed by faulted and folded mountainous arcs consisting of sedimentary rocks, metamorphosed rocks, and andesitic volcanic material. This complex geological history provides a more diverse and mineral-rich foundation for soil development than the basaltic or coralline materials that primarily form oceanic islands.12

In contrast, oceanic islands are typically smaller and often consist of either high volcanic peaks made of basalt or low-lying coral formations and atolls, which have limited soil depth and fertility. The continental islands' larger landmass and varied mineral-bearing geology allow them to support a wider range of vegetation and more robust ecosystems.123