An
increase in intra-abdominal pressure increases the likelihood of having a hernia. As Kenny Croxdale has pointed out, the belt increase intra-abdominal pressure. Also, as Kenny Croxdale pointed out, the only way to be all but certain to never get a hernia is to keep physical activity extremely low, because that will keep intra-abdominal pressure to a minimum.
Thus, if you are predisposed to getting a hernia, the use of a belt makes it more likely to happen.
Will use of a belt guarantee you suffer a hernia? No.
Will predisposition to herniation guarantee you will suffer a hernia? No.
Will refraining from using a belt guarantee you never suffer a hernia? No.
Does that mean you should never use a belt? No, it's up to you if the benefits outweigh the risks.
But the simple truth of the matter for these types of hernias is that the organ pushes through the weak spot very often as a result of increased pressure, and use of a belt is one way that such pressure can be increased.