It is difficult for people to throw things away.

Many things invoke "but this is a perfectly good..." I had a LaserJet monochrome printer. I knew I would never use it because I now have a color model, and if the color one broke I would replace it immediately. "But this is a perfectly good printer." It sat for a few years on a shelf before I finally tossed it. Resale nets too little to be worthwhile.

Other things represent work. This is old files in the office. My workplace was full of file cabinets with drawers of papers. It was decades of accumulated knowledge. No one would ever read them or use them. But throwing them away seemed disrespectful of all the work that went into those papers. For these things, I think of my daughter's math homework. It is extremely valuable and lots of work went into it, and there is zero reason to retain it the instant it comes home.

Other things represent memories. They embody a long friend or lost relative, or a vacation, or an occasion, or a feeling they caused when worn, used, etc. Discarding it seems to disrespect the memory. I try to keep these things to a minimum - keep representative samples, and digitize to the extent possible.

This is why discarding things is hard. I don't want storage space and have none, but I completely understand why people would rather shove apparently useless things into a storage locker. It's easier to pay to store it than to discard it. I go a step farther and say that it's worth it for folks to pay to store these things. It's worth $80/month or whatever it costs to have that stuff sitting in a storage box, even if they know they will never ever use or even look at them.

facebook marketplace for $10 or $20 is magic. People don't like free as much as they like paying $10 or $20 for a $50 item

Very well said, I often feel the same way.

About memories - throwing away the associated item often feels like admitting that you can't go back to the moment represented by the item. It's hard to face that small grief so it's easier to keep it there.