There can be many reasons why a person does not want to get involved with a stranger in a difficult situation. First, a stranger by definition is someone you do not know. If you do not know someone, why would you get involved with that person? For all you know, that person might be crazy. Second, we live in a scary world. Hence, fear is a real factor for most people. What if whatever is going on is a scam? We all hear about things like this. This fear may keep many people away.
If you change the perspective a little and consider other variables, you will see that there are many other possible reasons. Perhaps a person does not want to get involved, because he or she has other important things to do? What if that person is on his or her way to the hospital to perform a very important surgery? People have lives and things to do. This may prohibit them for getting involved. There are just too many variable in life.