isn't it common sense?
antibiotics inhibit the growth of bacteria, the only ones that grow are the resistant ones.. those resistant ones multiply and live on.
then the same antibiotics are used against the descendants and inhibit their growth as well but now in those descendants the ones who have superior resistance divide faster than the ones who have inferior resistance, since bacteria generations on average are about every 4 hours (1 divides into 2, 2 into 4/etc).. after a year of this you have a 2000th generation bacteria strain who is all but completely resistant to antibiotics. This is common sense and commonly known to any high school student learns about micro organisms (science/biology).
since antibiotics only help an organism's own defense system by slowing growth so it's immune system overwhelms the bacteria and not vice versa (which usually leads to death) it's not that big of a deal when used in people whose immune systems will completely wipe out the strain of bacteria being subjected to the antibiotics.. BUT when used on animals and then those animals are killed and used for meat, before their immune systems eradicate the bacteria, you've now put in place a system for generating super-resistant bacteria.
this also makes it obvious that you are purposely being obtuse about something that will affect millions if nothing is done.