Here's why:
* No definitive evidence: There's no concrete historical record of Homer's life or when he wrote these epics.
* Oral tradition: It's likely that the stories were originally passed down orally for generations before being written down.
* Dating based on content: Scholars estimate the events in the *Iliad* (the Trojan War) likely took place around 1200 BCE. This is why some say Homer wrote around the 8th century BCE, but this is very much an educated guess.
So, the answer is: We don't know for certain how long ago Homer wrote the *Iliad* and the *Odyssey*. It's likely they were written sometime between the 8th and 6th centuries BCE, but we can't be sure.