But why is it that only NASA can seem to prove it?
No one could really prove it without NASA to tell them that their theories were correct. Funny that.
They were, until the last few years, the only space agency with launch and operation capability in the US.
An analogy for you, Tom.
You live in a two-storey building with three others - Fred, Joe, and Sam.
Sam is the only one with a stepladder. You and the others do not have a stepladder, and you cannot afford one.
So you ask Sam to clean the upstairs windows, since he's the one with the stepladder.
Is there anything suspicious about this arrangement?
Substitute NASA for Sam and you have the reason why people collaborate with NASA to operate stuff in space.