How have we traced the appearance of HIV from monkeys? We get the flu from all kinds of animals, like birds and pigs. Those viruses make the species jump just fine. Yet all this time around cats, and FIV never made the jump, instead we got it from non-domesticated animals?
Is there information out there about the possible history of the virus itself?
HIV is believed to have come from monkeys because there is a similar virus, SIV, that infects monkeys and chimps. Genetic analysis reveals that they have a recent common ancestor. So the parsimonious conclusion is that HIV is a version of SIV which mutated to be able to infect humans, who are similar to monkeys. This probably happened when someone was butchering a freshly killed monkey or chimp.
As to why FIV never crossed the species barrier, who knows? Mutations are random, and it may be that right mutation has not yet happened in the right place at the right time. Or maybe it has happened, but the resulting infection was localized.
HIV/AIDS happened at exactly the wrong time, from the human perspective. Wars, poverty, and rural/urban migration were disrupting life in Central Africa in the 60’s and 70’s, allowing the virus to spread rapidly from whereever it initially crossed the species barrier.