Why is Christianity nearly directly identical to Mithraism…?
I don’t know if your talking about the same thing that I am familiar with, but what I know of it, it is not “hundreds of years older”, nor is it “nearly directly identical to” to Christianity. The Mithraic Mysteries or Mysteries of Mithras (also Mithraism) was a mystery religion which became popular among the military in the Roman Empire, from the 1st to 4th centuries AD. Information on the cult is based mainly on interpretations of monuments. These depict Mithras as born from a rock and sacrificing a bull. His worshippers had a complex system of 7 grades of initiation, with ritual meals. Little else is known for certain.