For me, the motivation comes from not being able to find things when I need them (which sometimes means I buy another one, so then have two of them), and from wanting my house to look good, which it does when it's tidy. I don't 'hoard', but I understand the resistance to throwing useable 'stuff' away.
The psychology of clutter is interesting, I think. I don't want to end up like my mum, who is always trying to offload her things onto others. She's always been the same - I may have mentioned the time she visited a 25 year old me with a bag of 'goodies' including non-matching rolls of spare wallpaper, a burnt saucepan and 25 pairs of chopsticks? The apple hasn't fallen too far from the tree (I still have - and use -the chopsticks😂), but my children are less tolerant of intergenerational junk and just say no.
My mum is as she is because she was a child in the war, and nothing was disposable. My only excuse is that I was brought up by my mum, so have something of the same mentality, but the difference is that in my lifetime there has been an exponential rise in the number of available items, and more spare money with which to buy them. I want a simpler life, but have been brainwashed by advertising and marketing campaigns that tell me I will be happier with X, Y or Z in my life. I know this, but it's deep-seated. I live with my husband in a family house, so there is room for unnecessary items, and they sneak up on me.
Husband is not the same, fortunately. He has his 'turf' - the garage and the shed - where he crams in his tool collection and other 'items that might come in handy', but on the whole the house doesn't suffer. There's just the CDs and DVDs he refuses to part with, and the pesky music stacking system that he thinks is valuable (it's not).
That's part of the problem, I think. Items that have cost us a lot can become sacred cows. The stereo system was expensive in the late 80s. It was bought as 'separates', which include a tape to tape deck, to record from one cassette to another, and enormous speakers of which he was very proud. It even has its own cabinet, in dark wood with a tinted glass door - I'm sure you can picture it. But technology has moved on, and you can get a great sound now in a much smaller machine that doesn't drive your wife insane and take up an alcove in the dining room. Those stacking systems, along with dinner services and 'collectible' ornaments are worth very little. Many people of a certain age have them, and the next generation don't want them, but it's hard to accept that something you saved for and have cared for for decades is basically 'junk', and was never the investment you thought it was (see also encyclopaedias). We are not losing money when getting rid of them - the money was spent when we bought them. In some cases it will cost to get someone to take them away, but it is a psychological leap to accept that.
I've really had to pull myself up short, stop trying to offload things onto all and sundry, and take responsibility for getting rid of them myself. I use freecycling sites, charity collection companies etc, and if they don't want them they go to the tip.
. I’ve just swept up the leaves in the back garden and now I’m sitting looking at some of the unpacking. Before I went away the time before last I had a blocked sewage pipe and couldn’t do anything for several days ( it resulted in an awful row with my neighbours which made me ill as I hate arguments) and the last time I had a steroid injection and needed to rest my leg for a few days. I think this is all down to being away from home a lot. I leave the house up there neatly tidy and spotless and come back to chaos, which exhausts me.
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