I imagine that routine use of antibiotics after surgery is covering up for a lot of this and is also contributing to antibiotic resistant bacteria showing up in hospitals with greater and greater frequency.
I don't think giving antibiotics after surgery as a rule is a modern invention.
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.