Quite simply because there is not ethical imperative to stop- and its about nourishment rather than just enjoyment.

Do we have an ethical imperative to stop cats from killing birds? All complex animal life on this planet consumes other living cells in order to survive, it is just a matter of scale and type.

This is especially true for animals that exist so that we may consume them. Hundreds of millions of chicken live only so that we may be nourished- similarly for cows, sheep and so forth.

Raising them in a minimally harsh and 'humane' environment can be an ethical good but that their lives are shortened by our 'harvesting' process is irrelevant, since they exist only due to that need to begin with.

Now killing an animal and discarding the resultant bounty- that is unethical and wrong, unless needed to ameliorate some other harm.