The most commonly accepted explanation of this is that the space agencies of the world are involved in a
conspiracy faking space travel and exploration. This likely began during the Cold War's 'Space Race', in which the USSR and USA were obsessed with beating each other into space to the point that each faked their accomplishments in an attempt to keep pace with the other's supposed achievements. Since the end of the Cold War, however, the conspiracy is most likely
motivated by greed rather than political gains, and using only some of their funding to continue to fake space travel saves a lot of money to embezzle for themselves.
In light of the above, please note that we are not suggesting that space agencies are aware that the earth is flat and actively covering the fact up. They depict the earth as being round simply because that is what they expect it to be.
