Why was Mark the first person to wrote a gospel when he wasn't there? Why did Matthew write his gospel off of Mark's gospel 15 years later, he was supposedly there? Why do they accredit books in the New testament to authors that didn't write them?

Why was Mark the first person to write a gospel? He may not have been the very first to write a gospel, but at least his gospel has survived to the present time, having been accepted into the Catholic-Orthodox canon.

Just as Mark was not the real author of the Gospel now known as Mark’s Gospel, Matthew was not the real author of the Gospel now known as Matthew’s Gospel. Given that this gospel appears to have been written in the eighties of the first century, its author was most unlikely to have been an adult already during the lifetime of Jesus.

Why do they accredit books in the New Testament to authors that didn't write them? The Church Fathers did not know who wrote the gospels they had chosen for the Catholic-Orthodox canon, but they believed they had to attribute their gospels to someone. They chose the names of four early Christians they believed might have been the authors, although we now know they were most unlikely to have been the real authors.