Hybrid big cats are artificial creations. They are unlikely to occur in the wild except in unnatural situations e.g. in very isolated populations where there is no mate of the appropriate species available. Because of the fertility issues, valuable genes may be lost by breeding dissimilar species together. Most conservationists condemn deliberate hybridization as wasteful in terms of genes and in terms of money. So why are they bred?
Many are bred out of curiosity. Exotic animals, especially ligers (the largest big cats on the planet), are great crowd-pullers. Pony-sized striped big cats and leopard-patterned lions are undeniably magnificent creatures. Others occur by accident where two animals are housed together from an early age in the belief that they won't mate with each other. The mating instinct is strong enough that a puma allowed herself to be mated by an ocelot one third of her size! This occurs where there is limited accommodation e.g. private collections, travelling circuses etc. Even experienced zoos have accidentally bred hybrids this way e.g. the servical. Believing that hybrids are always sterile, some keepers have housed a hybrid big cat with pure-bred big cats only to discover that hybrid females are fertile.
Speciation (one species evolving into two) is usually an excruciatingly slow process. Different species usually cannot mate and reproduce (reproductive isolation). If the species are closely related, such as certain cat species, they can produce hybrids, but those hybrids have reduced fertility. The more easily two species form hybrids, the more closely they are related in evolutionary terms. One way reproductive isolation occurs is genetic mutation. One group of animals might be geographically isolated from others of the same species. Each group accumulates slightly different mutations over many generations - some genes affect appearance, others affect behaviour. Many generations later, the two groups have diverged and are different enough that even if they can mate, they can't produce fully fertile offspring.
for more info's, you can read on the "Hybrid Cats" page, http://kennygilbert-simple-celavia.blogspot.com/p/hybrid-cats.html