I don't know why people work for Tesla/SpaceX. I can take a guess though - there are only a handful of companies that work in space related field and only a few companies that make electric cars. So it is somewhat understandable, if one really wants to work at these places.

Twitter is different - there are other big companies that provide as much tech challenges or more (whether they are better/worse than Twitter is another question). Twitter employees have many more options (relatively speaking) than SpaceX employees