It's a remote area and USSF has operations in nearby Ascension Island.
St Helena is where the minimum wage workers on Ascension come from. It only exists to provide cheap labour to Britain's Atlantic territories.
Because Trump, Musk, et al are hoping to live forever but their lifestyle is not very forgiving - hence all haste.
Y'all see Trump and Elon in everything.
Life extension is a popular area of focus and investment in the current crowd of powerful folks. They obviously don’t want it for everyone, musk even talks about how destabilizing it will be for broadly available life extension. See altered carbon dystopian life extension vision