The Original Autographs indeed no longer exist. Yet though, concerning your question, Crossnote, where you asked How is that so. This is how. By simply putting faith in God to keep His promise to preserve His word.
If God began His work of inspiration through penning down the Original Autographs through holy men of His, don't you think that God would continue to have His hand upon the entire process of the preservation, and translation of His holy word?
Think about it, Crossnote. At what point did God take His hand off of His word? At what point did God remove His hand from the process of inspiring, preserving, purifying, and translating His holy word, the Scriptures?
If God started the process, why do so many Christians today think that He would not finish it? Why do many Christians today think that God would somehow show indifference toward finishing His Bible?