Only because society wants it to be and people are too self centered to do something nice most of the time.
This kind of thing however does work to some extent occasionally.
Two summers ago I ran across two 20something guys with big extremely capable pickup trucks at a sand beach at Glen Canyon. People get their vehicles stuck in the deep soft sand there all day long. (The stuff looks and feels ok to drive on then 5 feet further you're up to your axles) These two guys go there once a year for a week and pull people out every day. They go swimming in the morning, pull people out all day, have beer and dinner at the campfire in the evening. They will take absolutely nothing from anyone as compensation for helping. They said they do it for karma points and to feel good about helping people in the world. I met them because I got my dumb butt stuck there and they yanked my 5 ton motorhome out of the sand like it was a toy car with just one of their trucks.
Last summer I was there and a family got their suv stuck in the same nasty sand. I quit swimming in the water and went over to help dig them out. A couple other people dropped what they were doing to pitch in getting this family up on a solid surface. When we were done and the family was parked up on the hill, we told them to just help others out if they ever get the chance. We were talking on the way back to the beach..and we all figured out that in the last few years, all 3 of us had been pulled out of the sand by the same two kids with the big trucks.