The discovery of an FIV vaccine was by no means quick. The virus itself was discovered/described about 15 years ago, not long after HIV. The recently licensed FIV vaccine is the result of at least 10 years of work.

In general, veterinary vaccines can be developed much quicker than human vaccines if for no other reason than veterinary vaccine candidates can, and often are, tested directly on the "patients". Vaccinate the cat, wait a few weeks for it to develop immunity if it is going to, and then administer virulent FIV to the cat and evaluate if it was protected from disease. We obviously can't and don't want to do the same type of direct testing in humans - i.e. vaccinate them with an experimental product and then intentionally give them HIV.

While HIV most assuredly did not come from FIV, and FIV most assuredly did not come from HIV, studies are in fact underway to evaluate whether a similar vaccine strategy can be used to develop a vaccine for HIV.

Who knows whether this could extirpate lions - I suspect not as there are many domestic cats that live for a long time with FIV. I think human population growth and habitat destruction is a far greater threat to lions.