Because they can! After all, in a money making conspiracy, you want to be spending unnecessary billions on such things...
Every scientist who design hubble must be in on the conspiracy, and every scientist who saw the pictures live, and all those involved in the launch, and all those who faked the pictures (also doing this pretty much live, and with flawless accuracy, revealing images consistent with theory, and a few anomalies for good measure)....and no it's not the same four guys. Literally hundreds, sometimes thousands of people are involved in these kind of projects, and certainly tens or hundreds of them are directly connected enough to be necessary co-conspirators. The scientific community is bigger than FEers seem to think.
In the space program, you need the astronauts, the mission controllers and the shuttle designers (who need to design one to go into high altitude flight or similar, while looking like it goes into orbit all for the minimum of cost). You also need the professional and amateur radio listeners and astronomers who watch the launches all the way to the moon and otherwise into space from many other world countries. I keep saying, this conspiracy has more in on it than not in on it!