This is a fair question posed by theists and atheists alike. The best we can do is speculate. It has been suggested that the New Testament might be better protected through copies than through original documents (Geisler).
If the original New Testament documents were all bound together that would mean that they would obviously all be in someone’s possession and they could potentially be changed or modified by the owning entity. However, when you have copies spread all over the ancient world, it makes it more difficult for any one scribe or priest or person who owns the originals to change things.
When the New Testament is reconstructed by copies and variants, the changes are rather easy to identify and can be easily corrected. In fact, just about all of the New Testament can be reconstructed from the Church Fathers who quoted it extensively in their works.
It’s a bit ironic, but not having the originals may actually preserve the New Testament better and keep it more accurate than having one solitary bound volume of all original New Testament books in one single volume.