There’s competing reactions, taking care of sick family/tribe members has obvious benefits and prior exposure is likely. Anyway, it’s hard to say how much of this is cultural, but multiple cross cultural aversions at least have the side effect of reducing contact with disease.

“Pathogen avoidance: Uncanny stimuli may activate a cognitive mechanism that originally evolved to motivate the avoidance of potential sources of pathogens by eliciting a disgust response. "The more human an organism looks, the stronger the aversion to its defects, because (1) defects indicate disease, (2) more human-looking organisms are more closely related to human beings genetically, and (3) the probability of contracting disease-causing bacteria, viruses, and other parasites increases with genetic similarity."[8] The visual anomalies of androids, robots, and other animated human characters cause reactions of alarm and revulsion, similar to corpses and visibly diseased individuals.[9][10]” https://en.wikipedia.org/wiki/Uncanny_valley

People’s near universal aversion to the smell of rotting flesh and human shit are similar examples. Of course at the individual level this is less universal. Another possibility is heightened pain response around minor skin damage compared to larger injuries. Aka thorns and paper cuts hurt so much because that kind of injury was actually more dangerous than moderate blunt force trauma which damages more flesh but doesn’t risk infection.

PS: That said it’s not like we can actually test these theories. It’s mostly an interesting idea that seems plausible.