There is a legal obligation, but it can be overturned if the creditor agrees to accept less than the full amount. Creditors are free to decide not to do so - &, as I said above, some do so decide. However, as PP said, many decide it is better to have a % of the total debt now than the - often uncertain - possibility of it being paid off over a long period. In any case, many creditors sell on debts for a small fraction of their face value, & they take that into account in deciding what they will accept. Better to have (say) 40% now than far less than 40% when it is sold on.
People get into debt for all sorts of reasons. Many of them are hit by changes in circumstances - eg health problems, relationship breakdown - & are just not in a position to pay off the debts. There is a difference between this sort of debt problem & people who just decide they won't pay. Yes, there is a moral obligation but it has to be tempered by a rational assessment of the real life situation. Creditors generally accept they can't get blood out of a stone.
In Myriad's case we don't know the full facts of how or why he got into debt, so I don't think it is reasonable to say he has a moral obligation to get his wife to use her money to pay his debts.