The man's explanation for the existence of the face on Mars was based on a pseudoscientific belief in an ancient civilization.
The man's explanation for why the face had to exist may vary depending on the context of the question.
However, based on the provided information, it seems that the question is referring to the belief held by a small band of individuals who claimed that the formation of a face on Mars was an artificial sculpture created by an ancient civilization.
This belief was not supported by scientific evidence and was considered pseudoscientific by most experts.
The probable question may be:
What was the man's explanation for the existence of the face on Mars was based on?