The real question is why science rejects the idea of God in the first place.
Science doesn't "reject" God any more than it rejects the plays of Shakespeare. To science, religion is simply irrelevant. Science and religion work different sides of the street.
Indeed. Science doesn't care about God one way or another. Science can only work with observable evidence, so until God gives us some, Science really can't be bothered to worry about him. If one day we find actual, hard proof of God's existence, that will definitely start being included in our scientific understanding of the universe.
People are free to believe what they want, as long as they acknowledge that it's a belief. No amount of faith can prove the existence of God. Likewise, no amount of science can disprove
the existence of God (at least not with our current understanding of how things work).