SpaceX does not seem to have a problem attracting talent and even poaching it from competitors.
The difference might be in the fact that Musk founded it and allegedly takes part in the recruitment process himself. Maybe he wants to do the same at Twitter. Turning an already existing company with an already existing company culture around is much more complicated, though.
SpaceX is going somewhere. Twitter is going nowhere.
This is a political play.
Musk may be a competent engineer, but he's used to being Emperor. He's completely out of his depth with culture and politics. So he's unprepared for the brutal muck-racking, humiliation, and character assassination that underpin political power games.
The "You can have free speech for just $8/month" accidental branding is already such a bad look. I don't see that he has the instincts, talent, or experience to even understand why - never mind to do better.
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.
Does Twitter have the ability to have a mission vision that people will sacrifice for? That's what keeps the recruiting pipelines full for the other companies and allows for the "we put up with Elon's BS" culture.
The difference might be in the fact that Musk founded it and allegedly takes part in the recruitment process himself. Maybe he wants to do the same at Twitter. Turning an already existing company with an already existing company culture around is much more complicated, though.