You also have to take into account that dealing with other people is much trickier than dealing with animals - and potentially much more dangerous.

Animals are simpler and predictable. There's only so much one can do to you if it gets aggressive - that's by selection, as if you found a wounded lion or other similarly dangerous animal, you'd likely shoot it dead rather than try and nurse it back to health. Can't exactly do that with humans.

Then, at high level, animal motivations are simple - avoiding threats, securing food, surviving. Humans can lie, cheat, rob you, or rape you. On the one hand, most people won't do that. On the other hand, real injuries requiring taking someone in are rare enough that staged ones are non-negligible possibility to consider. That, and acts of opportunity.

In short: humans are dangerous. If it were any other animal, we'd put it out of its misery too.

Fortunately, this too is something emergency services solve - instead of taking someone in privately, you need to, at most, shelter them short-term, and the moment you call 911 / 112, emergency response and law enforcement organizations of your country become involved, instantly granting you a large degree of protection. All that makes being helpful much easier than in the past.