OR they got expelled from regular (or other) obedience.In my experience, there are a variety of reasons:
They just didn't know any better.
Regular Freemasonry didn't offer the companionship and/or community service they were looking for.
They couldn't be admitted to regular Freemasonry in that jurisdiction because of felony convictions.
They have a family relationship in that obedience.
They want Masonic rank, which can often be bought.
They don't want to give up the masonic rank they have.
They got mad and left regular Freemasonry.
They got mad and left the prior irregular obedience.
They just don't care.