According to The Checklist Manifesto, antibiotics should routinely be administered just before surgery for this reason and has shown large reduction in mortality rates
Are you saying that after-surgery antibiotics can't be a cause of antibiotic resistance because we've been giving antibiotics for a long time? It takes on the order of decades for antibiotic resistance to be selected for enough that it becomes a problem. And the first antibiotic wasn't even discovered yet a hundred years ago.
Even if post-surgery antibiotics were the prime contributor to antibiotic resistance, arguing against the practice is disingenuous because there is no viable alternative.