Why dont the duke and king leave as soon as they have the 6000 in hand?

Aware that Pap is probably after his money (the $6,000 that he got from sharing the treasure with Tom), Huck goes to Judge Thatcher and begs the Judge to take all his money as a gift. The Judge is quite surprised by the request, but when Huck refuses to reveal why he wants to give away his money, Judge Thatcher agrees to "buy" it for one dollar, saying he will take the money "for a consideration."