Potbelly Pigs

I adopted some pot belly pigs from a guy who apparently didn't interact with them and so far after months of owning them only one let's us pet it the rest are terrified and I figured at first they'd eventually get used to us but after like 5 months they only get near me if I have food. Sometimes they get interested and smell my boot while I'm not looking but run away as soon as I look. I've sat multiple hours out there just trying to get used to my presence but they still avoid us