Lazy or mental illness

My wife is very sensitive about discussing my parents predicament. If I mention something new that they said to me, she immediately jumps in saying, "See they aren't mentally ill, their house is just a mess because they are lazy." She insists on this repeatedly. Her understanding is that if my parents were true hoarders, and this was out of a mental illness, then they would not be embarrassed to have visitors come into their house and simply not perceive the mess as others do.

"But they don't let anyone in! They are embarrassed! They know what they are doing."

I am not sure why it is so important for my wife to feel that the state of my parent's house comes out of laziness rather than a hoarding mental illness, but I feel otherwise.

Different Natures of Hoarding
I have a friend that is a social worker. He has been in a number of homes that are suffering severe hoarding. In one, as he talked to the hoarder, a cockroach ran across the piles of stuff on the table. He clearly saw it, and appeared surprised, while the person who lived there completely ignored the cockroach as thought it weren't even there.

This is the kind of mental state that my wife seems to be suggesting she would expect my parents to suffer from, interacting normal with everybody while remaining oblivious to the hoard.

The Overwhelming Nature of the Hoard
I believe the mental illness of hoarding manifests itself in my parents in a different way. They know that their house is a mess, and are not happy to show it to others. Yet they do not want to discuss it, leaving the mess as the elephant in the room. They create stories and excuses around the nature of the hoard, saying things like "I am working on it, just leave me alone." or "If you wouldn't bother us so much, then maybe we could get things done."

I see their mental state as that they know the hoard is there, but that they simple don't feel that they have any control over it. The hoard lives with them, but overwhelms them. Maybe even on some level they would like it to go away, but realize that it is not some external force that has taken up residence in their home, but something that comes from within that they lack the power to control.

Assessment
They are not lazy. They are overwhelmed by an illness that they neither want to admit to nor ask for help for how to deal with. So they remain stuck in the vicious cycle that this conditions wreaks upon their lives.