The "real reason" is two things:

1. Musk wants to attract young engineering graduates that will devote their 20's to working in his companies. These young people are highly talented and not yet smart enough to know that the pitch is absurd.
2. Musk wants to attract people with more money than brains to invest in his companies. People that are stupid rich and not smart enough to know that the pitch is absurd.

That's Musk's real target audience for almost all of his presentations, like the Tesla Robot. Musk isn't going to sell THAT many $20,000 humanoid robots. It's a gimmick to attract young engineers to come work for his companies.