I'm a typical IT pack-rat with cables, old PCs, laptops, many old parts. Hard drives are a risk since I don't want to toss due to not know what is on it (Bitcoin?) or have my personal data stolen, or just something I may miss copying from it.
My Dad died so much of his stuff is now essentially junk. But to me it's sentimental even things that I have no need for like his shoes, his clothes. My Mom tossed a lot of it out practically the day after his funeral. He has piles of tools, paint, gloves, coveralls.
Recycling rules. The local company makes it very hard for people to get rid of items. Much of it means you need a car to take it and drop it off. When there you enter a large building and some guy points to a pile and you have to drag it there. Anything big like wood has to be less than four feet in length and less than 40 pounds. Any elderly or those without a car or even a truck in cases like old mattresses are out of luck.
Just age and lack of stamina too or mentally not wanting to do the work of sorting through it. Mu Mom is nearly 80 and doing "The Big Cleanout" as older people do when they are nearing that time in life. But she tosses or gives away things at random without asking a family member if they want it.
There can be many layers to hoarding if it is that or just too much stuff or just being lazy I'm not sure where the line is.