My mom was a hoarder. She'd buy all the pants at the thrift store that fit my brother and me, because it was hard to find pants the right size. She kept stacks of egg cartons for art projects. She rescued dozens of animals, who peed on the abundant pants.

She bought multiple Saabs when I got my driver's license, because they have good crash survival ratings. She bought damaged vehicles at auction so the neighbors could repair and sell them. So there were just a bunch of busted cars on the property.

Once when I was a kid Dad tried to clean. She begged him not to throw away a small screwdriver, saying "it's my friend."

Nobody was allowed to come over because the state of the house and the property were so disgusting.

I'm not a psychiatrist, but for her it seemed to be a combination of totally absent executive function, emotional attachment to inanimate objects (to which she ascribed feelings of their own), and a desire to have a stockpile from which to provide. Add to that the happy side effect of protecting all of us from visitors and the massive inertia of the hoard that made it impractical to clean up even when she was lucid, and you've got an effectively permanent state of being.