I suspect on a large scale over time, post death donations exceed annual donations by quite a bit.
So, old uncle X dies, state fund stops paying his nursing home room in 3 days, after everything of value or mentioned in the will is picked over or set aside, its all gotta go somewhere and somewhere is three relatives with trailers driving to goodwill.
There's simply not the time to determine his 1970s suit is currently resellable as retro kool, his 1970s neckties are 50:50 resellable, and his 1970s fancy dress shoes are simply trash. You've got less than two seconds per item, times up, now help load up the bookcase its all gotta go and the sooner we're done the quicker this depressing job is over. Toward the end, people are like "box of old plates? I don't have time for this toss it on the Goodwill trailer".
Think of his neckties from the 70s, someone doing a 70s school play or costume party or maybe some kind of art exhibit might pay good money for perfect condition, and badly stained goes in the trash, now what about the one in between that's not perfect but better than most people's daily wear? People LARP on the internet about being experts on everything especially apparently clothing resales but we're kinda in a hurry here and my MiL is not an expert on that topic so she's seemingly randomly tossing stuff on piles for trash or recycle or goodwill, I mean she's trying but we as a culture do not license "cleaning up the estate of deceased relatives" so she's just gonna toss stuff semi-randomly.
WRT to hoarding, consider that red necktie thats a little worn and has a tiny stain on it. He wouldn't throw that tie out, because he was married to my long deceased aunt while wearing it 60 years ago, it meant a lot to him ... but not to anyone else and now he's gone. Or that hideous endtable, I mean, sure a 1960s collector might want it if its in perfect condition, but he never threw it out because it worked perfectly well even if nobody post 1980 would consider buying such a thing.
Oddly enough things are simpler with terminal patients. He handed his bible to his sister when he said goodbye so when its time for estate cleanup nobody has to wonder where the family bible is, its been at his sisters house a month ago. I suppose a surprise death might be more work. But, the cancer finally got him so just ship everything in the room that isn't food, to goodwill.