I don’t get it but it’s a legit illness.
It is definitely a mental health condition. My dad is a hoarder. My mom is an organized and clean person, and has managed to have him keep his clutter in his home office, an outdoor shed, their garage, and a storage unit. In his office you can get to his chair, desk, and printer, but there are paths that lead to them. He has office items stacked on shelves, tables, and the floor. He needs psychotherapy, but he will never get that type of help. At times my mom has made him go through his papers and discard the ones he doesn't need, which is most, and he gathers up a small group, and keeps the majority. She also has us children come over on occasions and throw some of his stuff out when he isn't there. He has so much junk, he doesn't remember all that he has gathered through the years. If he does find something has been removed or moved, it causes him distress. He has weird emotional attachments to objects, especially his work papers. He has IBM papers, manuals, etc. that date back to the 70s. It is like he has made them a part of his identity. If they are removed, he feels like he has lost a part of himself. It is bizarre, but it is very real in his mind.
Hoarding can be an OCD subtype. He will buy tons of an item if they are on sale, for example band-aids, and then he hangs them up in a bag in their garage. There are tons of items hanging in there unused, but they were a deal! Also if something like a beach chair breaks, he will not throw it out. He says he may be able to fix it later, but he never even tries. He just can't let go of it. It got to the point where one of us kids would have to take a broken chair while at the beach, and dump it in an unclosed dumpster location so he wouldn't dumpster dive for it. I organized the inside of their garage, which means I found new places for the junk, about three years ago so you could walk around inside and go from one side to the other, and it made him very disgruntled. I don't get along with him, and I knew I would catch his wrath, but I did it for my mom, and I didn't care how he reacted. I threw out a ton of his papers too, but he didn't notice, because there are so many. I did all of this when they were out of town. He was not happy about what I did, but eventually he got over the fact things were put into places that made it an actual functioning garage. He even likes having the space. My mom has made sure that it has been kept functional inside.
He knows that it is abnormal behavior, but as I said before, he won't get help for it. It does seem he feels shame when confronted about hoarding, but he mainly gets defensive, and makes a million excuses for why the junk should remain. My mother continues to keep it isolated to specific locations.
In his older age, he has mellowed on some things being discarded, but you can see in his face that it pains him. You mainly need to trash something when he isn't around, because he has some dementia now, so many times he doesn't remember so and so was even there.
I think with Nick's worker, moving some of the stuff to another location out of the way is possible. She will be upset at first, but the fact the junk still exist nearby may eventually relax her, and if not it can be moved back. I think she will eventually find that she likes the space, but she didn't have the mental power to free herself from what she feels is part of her (all her years of work collected in piles). If she does relax about it, then some of the stuff that is on the bottom of her junk piles can slowly be discarded, because she probably doesn't even remember what is all at the bottom of the pile(s).