rotten people

I often wonder just what is wrong with people. I was in town today, waiting for the bus home when I saw a woman walking down the middle of the road. She was very unsteady on her feet and nearly fell over the kerb edge. She veered back into the road where she was very nearly hit by a bus, then a taxi. When she reached the other side of the road she nearly fell over the kerb again. As she walked past me I tried to stop her and see if she was OK, but she didn't even seem to see me, and I couldn't get her attention. As she continued down the road she walked into a lamp post, and some teenage girls started laughing at her and making rude comments, but again she didn't seem to hear the girls. I was seriously concerned but when I glanced around people were either ignoring her or laughing and poking fun at her, saying she must be high on drink or drugs. I decided to phone the local police station, because I was worried that she would get herself killed on the road. As I did so I watched the woman try, and fail to get on a bus before she staggered off and vanished round the corner. I gave the police as much information as I could, about her appearance, her behaviour and the direction she was heading in, and the police said they would send one of the local teams out to see if they could find her and check if she was OK.
I just don't understand why people not only didn't try and help her, but were openly making rude comments about her. I mean, even if she was high on drink or drugs does that mean she deserves to be killed or injured, and ridiculed in the street? And what if she wasn't on something but was diabetic and suffering a hypo? Or that she had some other medical condition that was affecting her?
I know people may think I am a busybody but how can people stand back and do nothing when someone is clearly in danger? I would rather ring the police ten times about something that turned out to be minor than not bother ringing and somebody be injured or killed when making that call could make the difference.