At least one of which as a result of reposting it here.
There is such a thing as responsible rehoming, whether any of us likes the reasons or not. Supposing they are rehoming just because they got another pet, consider the scenario where they keep them but don't really want them and the pigs end up being ignored and neglected. I'd say finding them a home before allowing that to happen falls into the category of responsible rehoming.
It's important to remember that we don't know all the circumstances that lead people to make decisions to rehome their pets and can't get an accurate gauge from a single ad.
Sure, a lot of decisions to rehome pets are made without regard to the pets in question, but that just doesn't seem to be the case from what little is posted here, at least to my eyes. Regardless, no one deserves to have their ad trolled and reposted because you don't like the content. They obviously aren't breeding. Responsibly finding a home for pets they no longer want is something more people should do rather than dump them in shelters. Expecting people to justify and explain their situation and choices when they post an animal is counterproductive to finding these animals a good home.