It would be tempting to say that mini-pigs have become trendy pets, but they haven't. It's impossible for something to be popular when it doesn't exist.
When people hit the internet looking for "mini-pigs," they often find websites for special "breeds" of miniature pig. The websites offer pigs that are under 35 pounds, or even under 12 pounds. If that sounds ideal, well, so does a supplement that lets you lose weight without exercise or a job that lets you earn a thousand dollars a day in your spare time. There are websites that offer those as well.
There is no breed of pig that's a "mini-pig." Vietnamese potbellied pigs are the most popular pet breed and they can get up to 300 pounds. Careful breeders can get the average size of a small-breed pig down to between 70 and 120 pounds, but there's no guarantee, when buying a piglet, that it won't get even bigger than that.
So how do people think that mini-pigs exist? Although breeders can make decent money selling supposed mini-pigs, they are still rare pets, so the people who get scammed are few and far between. Often, those people won't own up to being scammed, since most of these pigs have to be either given to sanctuaries or put down when they outgrow their intended weight. A few people get undersized pigs, who are sickly due to inbreeding. And some extremely unscrupulous breeders recommend undersized food portions, to starve the pigs and keep them small. This rarely works. Most people will figure out that the pig needs more food. Starved pigs get aggressive or just never stop screaming for more food.
So, if you were hoping for a cat-sized pig that will trot around your house contentedly grunting, modify that hope. If you can't handle a very big dog, don't even think of getting a pig.