It's not given to sick animals, it's constantly given to all livestock because it's cheap and it's seen as a sort of "preventative maintenance". Which is bad for all kinds of reasons 1) a lot of it makes it into your meals 2) it reduces the efficacy of antibiotics by constantly exposing it to bacteria (allowing them to eventually become resistant).
Probably other reasons it's bad as well (I'm also not a doctor and just write code).
Giving antibiotics to animals also makes them grow bigger.
It's billions of Petri dishes. It's a white swan in the making.
It's really a shame that now humans are not given antibiotics to combat antibiotic resistance, when humans do not even consume most of the antibiotics produced.
Not all antibiotics and diseases are the same. It still makes sense to not overprescribe powerful antibiotics that humans use for human diseases. Even if agriculture is recklessly using cheap antibiotics in animals.
Probably other reasons it's bad as well (I'm also not a doctor and just write code).