>>298162Plenty of reasons.
First of all for milking you need the subject to be cooperative.
Cows don't care that much, most other animals do.
Second is ease, most cases milk won't come out by itself unless the tit is succ. It is not that easy to get milk out of tits except when they get succ
So yeah it's neither easy nor efficient. Also most females across whatever specie will most likely get angry at you if you try to milk them cuz biologically they are wired to only give milk to care for their offsprings or some shit.
Really cows are the exception because they are unusually cooperative and produce tons of milk.
Even goats are hard to milk, idk how ppl manage.
But yeah kinda strange nobody tried milking pigs. Likely people have tried and it just didn't work lol.