They were chased and killed by humans. Stranded on an alien planet they desperately tried to return home.
They knew their existence was doomed and therefore they wrote down their story for others to read.
They wanted to tell us who they were and what brought them here.
They left a message for future generations, but the alien artifacts they left behind were hidden from the public!
This story is known under a lot of names and it is one of the most covered-up stories in the history of extraterrestrial-human interaction.