Also, SpaceX promotes itself as very mission focused and exciting. By doing so they end up getting the best people.

Among Musk's successful customs in running his businesses is going above and beyond in recruiting. He is very personal and direct with every hire he goes after, as he seems to understand or at least recognize the substantial difference in the 5-year out outcome of a company between getting someone who is 99.9th percentile vs 99.99th+ percentile.