I think it might mostly be an instinctive behaviour.

Self preservation is coded into us, just like every other living organism. The problem lies that we don't have to physically fend for our lives, like if we were uncivilized, but the urge to keep yourself "safe" remains. So you do what you must to "survive", or to "protect" your future.

We've learned that it it's a good system to think about more than oneself, but it's not always that easy to do. Your technically going against your instincts. That's why many people might do what's "right" when someone's looking, but if there were no witnesses, the path chosen might have been very different.

Now I'm not trying to defend the cruel, heartless behaviour of some people against others. We've been civilized for a long time and there should be something in the back of your head telling you that maybe you should take others into account in your decisions. You can still think rationally, like an addict might have to, to not get another fix.

Well, that's my bit about it. I hope I've helped a bit, and if not, I hope you find the answer your looking for. 😊