Super Mario 64 was one of the first video games released for the Nintendo 64, Nintendo's first completely 3D video game console. Through trial and error, developers created one of the greatest video games of all time and they knew this, so Super Mario 64 was shown off many times to the public. This gave people the opportunity to take photos of it's development more than they could of other games, which allows us to see the many changes Super Mario 64 went through.
UPDATE - As Of March 6, 2014. Beta64 Talked About The Super Mario 64 Beta