Because one day our development would reach a highly advanced technological status
Being wanted to leave behind some type of a message
A type of secret code that needed to be deciphered by a future generation
That understood or would understand what really happened in the past
And that generation is us
From the TV-series 'Ancient Aliens' Season 3, Episode 13, 'Aliens and the Secret Code'
The 'We are a species of explorers' line comes from Season 1, Episode 5, 'The Return'