Partially the answer to this question is that biodiversity protection involves a wide variety of interventions, some presumably effective, some not, and across all those interventions it is not clear how neglected the cause area actually is.
However, a bigger reason might be the inherent conflict between traditional environmental protection, focusing on biodiversity, and the animal welfare/liberation movement. The latter is a lot more prevalent in effective altruism, through organizations like Animal Charity Evaluators and Wild Animal Initiative. There are some sources I can recommend to help clarify the nature of this conflict, starting with “A Triangular Affair” by J Baird Callicott, and “In Nature’s Interests?” by Gary Varner, but briefly: if wild animals are moral patients with rights, it is not clear that their status as this-or-that-endangered-species matters very much, and vice versa. In EA, we tend to focus on the experience of animals as a neglected source of suffering, and that does trade off against biodiversity concerns.
Finally, the philosophical case for why we should value biodiversity isn’t clear-cut, although I certainly share your intuitions about it! This is an essay from a biologist in the community about what might be valuable about biodiversity and how mainstream environmentalism might be getting it wrong: https://eukaryotewritesblog.com/2018/05/27/biodiversity-for-heretics/
Partially the answer to this question is that biodiversity protection involves a wide variety of interventions, some presumably effective, some not, and across all those interventions it is not clear how neglected the cause area actually is.
However, a bigger reason might be the inherent conflict between traditional environmental protection, focusing on biodiversity, and the animal welfare/liberation movement. The latter is a lot more prevalent in effective altruism, through organizations like Animal Charity Evaluators and Wild Animal Initiative. There are some sources I can recommend to help clarify the nature of this conflict, starting with “A Triangular Affair” by J Baird Callicott, and “In Nature’s Interests?” by Gary Varner, but briefly: if wild animals are moral patients with rights, it is not clear that their status as this-or-that-endangered-species matters very much, and vice versa. In EA, we tend to focus on the experience of animals as a neglected source of suffering, and that does trade off against biodiversity concerns.
Finally, the philosophical case for why we should value biodiversity isn’t clear-cut, although I certainly share your intuitions about it! This is an essay from a biologist in the community about what might be valuable about biodiversity and how mainstream environmentalism might be getting it wrong: https://eukaryotewritesblog.com/2018/05/27/biodiversity-for-heretics/