https://www.scientificamerican.com/article/when-same-sex-mating-makes-reproductive-sense/

When a male sand-sifting sea star in the coastal waters of Australia reaches out a mating arm to its nearest neighbor, sometimes that neighbor is also male. Undaunted, the pair assume their species’ pseudocopulation position and forge ahead with spawning. Mating, pseudo or otherwise, with a same-sex neighbor obviously does not transfer a set of genes to the next generation—yet several sea star and other echinoderm species persist with the practice.

They are not alone. From butterflies to birds to beetles, many animals exhibit same-sex sexual behaviors despite their offering zero chance of reproductive success. Given the energy expense and risk of being eaten that mating attempts can involve, why do these behaviors persist?