Well, they are the source of the corrupt texts that the modern bibles are now following.
Your point is interesting, since the translators of the Textus Receptus (KJV) did not view the variants (and there WERE variants) the same way you do, nor did the view the TR as the "preserved" version. They were pretty much of the same mindset of modern scholars, viewing all the texts with differing degrees of reliability, including tha TR. You also had your liberals (although they were far fewer in number than today) who did not hold any reverential awe for the book.
The idea that God preserved His word through the ages is an indisputable fact, and a lynchpin of the faith. The idea that this was only through the Textus Receptus is ignorant and uninformed. Not even the translators of the KJV believed that. I used to have a collection of quotes from some of those guys illustrating that, but I have misplaced it.