In other words: If so many planets that were created in different locations and under different circumstances show the same property, it’s likely that our own planet has the same property as well. All of our observations show that other planets are spherical (and since we know how they’re created, it’s also obvious why they take this shape). Unless we have a very good reason to think otherwise (which we don’t), our planet is very likely the same.
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.