Because going to space as a private citizen is hard.
So are a number of other endeavours, none of which seem to find a lack of acceptance from the FE community.
Photos from space are disbelieved without personal "private-citizen" verification, but when it comes to (for instance), the setting of a land-speed record, water-speed record, or other such, this is seen from afar, and third-party accounts, photos, video, even the reporting by Guiness, are all accepted at face value. I could name a host of other scientific achievements, all outwith the scope of the private citizen, which are also taken at face value, without verification.
Yet the "I need to verify it for myself" attitude persists amongst the FEers... Why is it this topic in particular that brings out this attitude?