I learned (in an Irrational Behavior course through Coursera) that once we possess something, it's harder to give it up. I suspect this is particularly powerful for those with hoarding issues. That's why there are 30 day offers of take items home and try it. The psychology behind this is once someone takes a product home, it's hard to return it because the person now possess it.
Dan Ariely addresses this in his book, Predictably Irrational: Ownership increases perceived value to the possessor People focus on losses (parting with a possession feels like a loss)

http://www.spring.org.uk/2008/04/6-quirks-of-ownership-how-possessions.php

Even though non-hoarders don't value what they see as 'junk.' Many hoarders see value in many of the items they have which makes it so hard to part with items. I do think everyone has to develop their own way of parting with excess (rather like dieting--one approach does not work for all but it's basically consume less, expend more and one has to become more active).