Because hybrids are maladaptive, they have lower survival rates. They would most likely live shorter lives and leave no descendants. That is precisely what we see in nature. We don't see large numbers of coyote-wolf hybrids. Instead we see coyotes and wolves in large numbers but comparatively few hybrids. This example is repeated everywhere in nature, with rare exceptions, so what we observe is very low incidences of interspecific hybridization. Even though many duck species can produce hybrids, they nevertheless rarely hybridize, as the scientific collection of duck specimens by natural history museums like Harvard's Comparative Zoology Museum have shown. Because hybrids have lower fitness, their parents also have low fitness. It means those individuals who cross species boundaries to interbreed with other species will leave fewer young. The result is that those individuals that do observe species boundaries are more fit and will leave more young. Therefore natural selection often result in the appearance of premating isolation mechanisms, which are ways different species identify themselves as the same species to each other to prevent interspecific hybridization. Additionally, natural selection also makes sure that individuals do utilize these isolation mechanisms and remain faithful to their own species. Each species often have elaborate mating rituals, and only those that can show they are the same species by executing these rituals will be selected as mates. Those individuals that ignore the premating isolation mechanisms will often pay the price and leave fewer or no descendants.
