I had a fairly significant surgery at a premiere US hospital including several days of recovery in the hospital and didn’t get any antibiotics after the fact. They could have injected me with something during the actual surgery, but it didn’t show up on the bill.

I think this may be specific to Heart surgery.

I was given prophylactic antibiotics for prostate surgery. It might depend on the surgeon.

a lot and a heart artery drip for 30 days are orders of magnitude different in quantity

A friend underwent operation of his aorta. Post-surgery inflammation is an absolutely common complication and they dumped a lot of antibiotics into him precisely to reduce the risk. (If I understand correctly, it wouldn't be probably fatal, but very, very unpleasant.)

It is.

I think blood flow to the brain >> impacts of antibiotics is the likely order of magnitude of impact - though tough to tell.

correlation causation

Whenever I had (minor) surgery in France, I was given antibiotics "as a shield". I obviously do not know if this helped or not.

Now, French doctors were always very quick to prescribe antibiotics (as a kid I had plenty of them) and it took quite a lot of effort to change their(and parent's) mind. My children got much less, though they were almost never checked for virus vs bacterial infection.