Cozzyd is right:
> The Wall Street Journal reported citing people familiar with the matter that SpaceX lawyers recommended that the company's leadership not pursue a higher security clearance for Musk because he would have been asked about contacts with foreign officials as well as his prior drug use.
https://www.foxbusiness.com/politics/why-elon-musk-doesnt-ha...
(Didn't link WSJ article due to paywall.)
Your link confirms GP is correct:
> Musk holds a "top secret" clearance that gives him access to some of SpaceX's sensitive programs.