I think the difference is SpaceX doing cool cutting-edge things with rockets. People want to be a part of that and are willing to take less pay and poorer working conditions to do so.

Twitter is boring. Its explosive growth days are behind it, working there now is basically about maintaining a legacy platform that has a bunch of problems that mostly aren't technology problems. It's about as interesting as working for a big insurance company; if the paycheck and working conditions aren't there, you're not going to be able to attract talent.