Demon possession in the Bible?

Why is it that there is nothing in the Bible that cannot be explained by science? For example, the demon possessed people mentioned in the New Testament that Jesus and his disciples expelled. Was this really demon possession or neurological disorders such as up Tourette's Syndrome or Epilepsy? To a person living 2000 years ago Tourette's Syndrome was not heard of. Although, it was there, and epilepsy was present as well but they did not know of these disorders, the superstitious religious followers most likely misdiagnose a neurological disease for demon possession. I would like to hear your response . Thank you