How rare is it for an animal to kill and eat a person?
Rare enough that a single case can become a scientific publication. A forensic overview of animal attacks on humans describes three autopsy cases and singles out one in particular: injuries attributed to predation by red foxes (Vulpes vulpes). The authors call such cases rare and note they are an underexplored area of forensic literature, which is why the case was considered especially noteworthy [2].
That framing matters for the question. The paper does not claim predation on humans never happens; it says attacks by wild and domestic animals are a real public health issue that causes deaths and hospitalizations, with rates varying by local wildlife and cultural practices [2]. So the accurate picture is not "animals leave us alone" but "predatory attacks are uncommon relative to the enormous number of human–animal encounters, and true predation — an animal treating a person as food — is rarer still."
Why people make difficult prey
The evidence points to context rather than a single cause. The forensic paper notes that urban expansion, shrinking natural habitat, and more human recreation in wild environments are increasing human–wildlife interactions and, with them, the number of incidents [2]. In other words, the rarity of predation is partly a matter of separation: most people most of the time are not where large predators hunt. When that separation shrinks, encounters rise.
Size and social behavior are the other side of the story, though the supplied papers support this only indirectly. A six-meter reticulated python discovered in an urban area of South Sumatra, Indonesia, is presented as a massive animal whose notes include humans as prey [1]. The fact that such an encounter is written up as a notable observation is consistent with the idea that even very large constrictors rarely take people, but the abstract does not establish why. It is safer to say the case illustrates that human predation by big snakes is possible and unusual, not that pythons routinely avoid us for a specific reason.
What investigators actually have to sort out
When a body is found with animal injuries, the first job is not to assume predation. Forensic pathologists must rule out a homicide before anything else, then distinguish injuries inflicted before death from scavenging after death, so the cause and manner of death are interpreted correctly [2]. This is a useful window into why genuine predation is so rarely confirmed: an animal feeding on a body is not the same as an animal having killed that person, and telling the two apart takes careful work.
That distinction also explains why the literature is thin. Cases that survive that scrutiny are few, and each one is reported because it adds to a small body of knowledge [2]. The reticulated python record fits the same pattern: a striking individual animal documented in an unusual urban setting, with notes on humans as prey, rather than a study of routine predation [1].
What these cases can and cannot tell us
Neither supplied paper sets out to test why humans are rarely preyed upon. One is a forensic case series and overview emphasizing the rarity and diagnostic difficulty of animal attacks [2]; the other documents a single large python and its notes on humans as prey [1]. Together they support the claim that predation on humans is uncommon and that confirmed cases are noteworthy, and they show that encounters rise as humans move into wilder and shared spaces [2]. They do not measure how often predators encounter people and decline to attack, and they do not compare human prey rates with those of other large animals. The honest answer to "why" is therefore a combination of separation from predators and the difficulty of taking a large, group-living animal — with the second part inferred from the rarity of documented cases rather than directly demonstrated in these papers.
Sources used in this answer
Figure 2. A massive Reticulated Python Malayopython reticulatus, approximately 6 in Notes on Humans as Prey of Reticulated Pythons Malayopython reticulatus (Serpentes: Pythonidae) in Indonesia
A roughly six-meter reticulated python was found in an urban area of South Sumatra, Indonesia, and the report includes notes on humans as prey of this species.
Vulpes in Fabula: when human becomes prey – case report and overview on animal predation
Animal attacks on humans cause deaths and hospitalizations and are rising as urban areas expand and people spend more time in wild environments, but confirmed predation cases such as one attributed to red foxes are rare and underexplored in forensic literature.