The publishing industry doesn't take kindly to plagiarism, and people in this business have long memories. Again, not so. Nor are established authors interested in rewriting the books of others. The economics of publishing and theft are in direct opposition. Theft is practical only when the stolen item can be disposed of quietly, without attracting attention.
Books are profitable only if they can be marketed publicly, attracting lots of attention.
Publishing entities are in too much danger of being sued for plagiarism as is to risk actually committing it. We all find our manuscripts precious. It is often difficult to understand why agents, editors, and publishers don't share our view. This doesn't mean that amateur writers don't face risks in the marketplace. Those who prey upon the unwary and the desperate, however, don't do so by stealing your manuscripts.