Work gives people self-worth
I guess the idea is if robots and AI automation takes most of the jobs in the world, governments will institute universal basic income. This will theoretically free people to pursue their passions in life. I'm not sure that is the case given so much meaning and self respect is tied to feeling useful and accomplishing things with work.
And then there's the innovative side. People want to start businesses to make fortunes and help the world. I can't see that fundamental aspect of humanity being entirely replaed by AI.