Humans being humans. I believe that some of this at its core is behavior hardwired into us from the earlier days of our evolution. Someone is always going to want more than someone else. Some of them will be entirely willing to accomplish that through the use of force or through thievery. That certainly happens in the animal kingdom, and we are animals ourselves. Yes, we could probably provide an equivalent existence for the entire population, but people in the developed nations are not going to lower their own quality of life by any significant amount therefore it's not going to happen. Not now anyway. If we get to the point where we can elevate everyone, then maybe.
A lot of us are doing what is basically busy work. It's not necessary, but as a people, we wouldn't know what to do with ourselves outside of work. Look at the sad lives of people who win large lottery prizes. Some end up worse off than before. I know of people that would qualify for disability, as an example, but they don't for the same reason. Look at areas where a lot of people live on entitlements. They tend to be high crime areas, do they not?
We could get there maybe, but we're not ready for it now.