It's not that diamond gobies are naturally short-lived. They have very specialized eating habits and usually starve to death in captivity, because most aquarists can't provide for their needs. But people think that they "need" a sand-sifter to keep their substrate clean (usually because they've been told that they do), so the aquarium industry keeps selling them. It's a marketing scam, really, and a shame, because countless numbers of fish end up suffering.