The thing, is, a lot of people think they are doing something for rare breeds by buying and keeping them, but, unless they are registered as pedigree stock, they don't count.
Okay, so in a small way, you are helping those breeders who do help conserve the breed and bloodlines - because you are buying their unwanted stock which don't come up to the breed standard (and therefore should never be registered). You are also helping to pay their ongoing feed bills (which will be considerable) and helping them keep their respective herds going.
However, for those people who care about conservation but who choose to breed from unregistered stock, they might as well be buying cross-bred pigs from the market. That does nothing to help any breed. Ask the British Pig Association says, quite correctly: "A pig without a pedigree is just a pig."