Why are unidentified people called John or Jane Doe ?

because jane doe is a uncommon name so they use that then if it is a boy they call him john doe if it is a boy

In the USA, the name John Doe is used for a defendant or victim in a legal example or for a person whose identity is unknown or is intended to be anonymous. Male corpses whose identity is unknown are also known by the name John Doe. A female who is not known is referred to as Jane Doe. A child whose identity is unknown is referred to as Precious Doe or Baby Doe.

cause its John and Jane were popular names back then, Doe is another word for unknown I guess

because John Q Public was taken

They relate as the most common names

Its a way to be respectful and give a name to the unknown

It's easier to spell than Stephanie or Johnathon.