There's quite a lot of confusion about this question here.

You are right that debt of this type are individual and other parties (spouses, heirs) can't be pursued for it. But it has to be taken into account in a divorce.

Johnny and Janey have a $1m property, $200k savings, $200k retirement between them. They should each get $700k from a divorce (assume they were penniless students when they got together and acquired all the assets during the marriage).

If Janey* wants to stay in the house, she only has to borrow an extra $300k to buy Johnny out. That plus her share of the financial assets, pays for his share of the house.

Now Johnny reveals that he owes half a million in credit card debt that he never told Janey about. She can't just say "That's your problem, it comes out of your share." The marital assets are diminished by that amount before division.

Janey now gets $450k, an even split of the net assets. She has to come up with $550k to keep the house, effectively paying off half of Johnny's gambling debt as well as buying out the difference between the house and the financial assets.

If she doesn't try and keep the house, the cash she gets represents half of the assets minus half the debt. If Johnny owes $2 million, the married couple together are $600k negative. For her to leave the marriage, she has to pay half of this towards Johnny's debts. So she will have to come up with $300k cash to give him, on top of losing all her assets.

Of course, Janey married Johnny for better or worse, and that includes his gambling addiction. But it might feel unfair to Janet, especially if she didn't know about the gambling and couldn't have done anything to stop Johnny running up the debt. And Johnny's lawyer makes sure Johnny dredges up everything he owes in the negotiation, the opposite of the situation with assets where a sharp lawyer might tell Johnny to tread lightly owning up to his gold coins/offshore account. In the worst case Johnny hits Vegas when the divorce seems to be inevitable, knowing that the losses will go into the joint pool, whereas his winnings can be spent on partying or pocketed in cash.

* Divorce participants' behavior is stereotyped by gender. Apologies to all the thrifty houseproud Johnnys and louche deadbeat Janeys out there.