Why do pigs have tails? They're too short and curly to be useful for anything.
> can't swat flies like a cow or horse
> not useful for balance like a cheetah or greyhound
They'll have some sort of vestigial tail, but in the case of domestic pigs, evolution is a controlled process, so much like dogs, they'll have whatever traits we breed for. Or Monsanto will step in and they'll just be a huge slab of bacon with a mouth.
Because pigs are man made.
We bred them for centuries to their current state.
Look at a warthog's tail.