The thing is, as the OP says below, whatever you think you might get from it on eBay or whatever is a bit of an illusion. First because those kinds of collectibles are overpriced on eBay and don’t sell for the prices they are put on at anyway. Easy to get excited because people have their mum’s Lilliput Lane collection on eBay listed at £300; but if you look at what actually sells, the ones that sell make a couple of quid. Everyone’s doing the same, and just waiting for that sucker who wants that exact thing and will pay that exact price, but in reality there’s not really a market for this stuff so you could be waiting for years.
Second, because eBay selling generally takes ages - months or years to clear stuff like that, and in the meantime you have to store it, so it’s cluttering up your space instead which you try to sell it. Then if you cost your time in photographing, listings, managing your eBay account, packing things up and trips to post office, etc., it takes up a huge amount of both time and mental headspace. Often the money you make, after PayPal fees and so on, is not really worth your time listing and selling it. If you had no job and nothing else to do all day it might be worth doing for the money, but if you don’t have much time, it isn’t cost effective to spend it doing this for little joy and very little return.
Third, as above, it’s a long process that takes up your time and mental load for ages in contacting dealers, cleaning and storing things, listing them, waiting to sell them, in the meantime taking stuff to charity shops and the tip and everything else. It’s a slog; exhausting! You could spend a year clearing a house of things like this (and probably at a time when you need to get a house sold for either probate or care home fees, and just haven’t got that time.) In the end you might as well give it all or throw it all away, because the money you’d make compared to the time and effort you spend, and the emotional and physical stress of having all of this fill up your own mind and time.
It really is falling right into the same trap to think you can recoup money for stuff like this. That what led to it all being hoarded in the first place! And then all that stuff is just going to occupy your house, and your life, while you try to fruitlessly make tiny bits of money back from it. A recipe for your parents’ folly and their hoarding dominating your own life for years from beyond the grave. Awful!