I don’t know how that got started. But if you order the “home sale kit” which includes a statue of St. Joseph it will also include a novena. It explains to place the statue anywhere in your home (like any other statue) and ask St. Joseph to intercede for you. He is the patron saint of families. Moving and selling/buying a new house can be trying times for families so that’s a good reason to appeal to St. Joseph I suppose!
As far as burying the statue, again, I dont know how that got started, but someone once offered the argument that it might be a leap of faith.
Anytime we’ve moved, I just ask him to pray for our family.