I remember i worked for Wood Group, and they renamed themselves as ‘Wood’, which i thought was a bit random. After asking the managers, i asked why the one word company name.
They said that they wanted to be like Virgin, where Virgin is the Brand, and the the companies file under it, Virgin Music, Virgin Money, Virgin Atlantic etc.
So looks like Musk is maybe trying to align his companies under the brand name X. So Space X, X (twitter) etc. Just have to rename Tesla, Starlink etc…