It led me to spend a lot of time considering what causes their behavior.
Not only do they hoard, but the process of hoarding also inflicts psychological damage against their close family.
I think it is a combination of self delusion and obsessive control.
Self delusion: The hoarder tends to believe each item they have kept has value or will be valuable someday. Almost as if for each item kept, it is the equivalent of having an unclaimed lottery ticket that will win eventually. Now, try convincing someone to throw away a lottery ticket before the date of the draw.
The interesting part is the hoarder would not sell the item, even if it was found to be very valuable (most 99.9% is junk). It is about the items perceived value.
Strangely I've seen many instances of hoarders have something of real value only stashed amongst a heap of junk and not stored appropriately (damaging the item in the process through neglect over time)
Control: This aspect is about controlling the situation and those around them. They are not interested in anyone else have a say in the matter.
There is a complete lack of empathy toward those affected by the consequences of hoarding (family etc)
The hoarders I've met tend to be very intelligent and manipulative (and verbally abusive) if they suspect someone is going to try impress change upon them. (A situation they perceive to not be in control)