Industrial meat farms operate a model called Confined Animal Feeding Operations (CAFO). This means that producers cramp animals in tiny cages, where they do not have enough freedom to move. Situated very close to each other to save space, the cages force animals (sometimes) to spend their whole lives in one position.
Because the distance between animals in adjacent cages is small, disease transfers between them easily. Just look at how SARS-CoV-2 emerged in China – virus jumped from one animal to another and then to a human for exactly same reason – proximity.
The reason for cramping more animals in a small area is to increase profit per square meter of the occupied section. The land is scarce, so companies maximize its use.