Simplemind, i'm sorry for the pain you went through with your parent's house.
I am an instrumental hoarder. Actually I fit in several categories. I think that the tendency toward hoarding is innate, but how it is expressed is a product of your environment - "learned". As a parent, teacher and artist I have many opportunities for my instrumental hoarding to bring me reinforcement and dig a deeper channel in my brain. My dd called home from college her freshman year and said " I need 100 identical items to build an art project out of and I have a $5 budget." I was able to give her choices! For free! Happiness! Pride! The pleasure centers just lit up. My fellow teachers know I am their go to girl. - social status!
You need a lot of people on your cognitive behavioral therapy team. I am lucky because I have a lot of people who love me and understand me and will take the time to help me make new paths even when it seems ridiculous. In some ways it's like physical therapy for a severe injury. Only you can SEE the physical effects of an injury, so you don't feel stupid or frustrated when you tell a full grow person "great job! You got three beads on the string today!" or whatever. Today my daughter's boyfriend asked if cd cases were recyclable. And I said "no. You have to throw them away. And if you save them, it doesn't make them not trash, it makes your house the dump.". And my non-demonstrative daughter got up, walked across the room, wrapped her arms around me and buried her face in my shoulder. These are the things I hold on to when I'm trying to throw away the trash. That is worth way more than $5. My coworkers can go buy craft supplies.
Ultralightangler, I'm not so sure about the trauma theory. I think there can be a lot of small "traumas" that aren't really traumas to normal people, or even large traumas that push you one way or another - usually they intensify the hoarding behaviors, like an addict reaching for more, but maybe sometimes they can also be wake up calls. And I think in some cases, the behavior just slowly takes over your life until you reach a tipping point and give up.
Libby, religion can also be seen as a learned behavior, but whatever culture a person is raised in, I think some feel a deep connection to the divine and others nothing. Those who are deeply devout might have taken a different path in a different culture, and may even convert, but are unlikely to "unlearn" religion.