>>torgin+(OP)
I had a look at SpaceX career page. There are 128 software related roles available. Perhaps half of those could be filled by big tech type companies, the others are more specialized (like antenna software engineer). I don't think that 64 open positions would move the needle really. And, if it were that easy to get around the security clearance by having another company, he could have created a new / separate company years ago.
Wouldn't a simpler explanation be that SpaceX is making a lot of money while xAI is losing a lot. If funds have to flow through Elon personally it is likely complicated and costly. Also, if the "space data center" idea is actually workable (I have no idea if it is) then it does make some logical sense as well. Of course, Twitter just seems like kind of a write off to me at this point.