I have spent that sort of money on a knife...a folder or two and one fixed blade. The fixed was my one and last experiment with collecting.
If one makes, it is hard to buy hand made from someone else. There is a chap here selling an AEBL Ben Orford Parang, along with a bunch of other Orfords, and I would dearly love to have it. It is expensive. I would want it as a tool and it would get used and used hard on occassion...but, I also want to make my own parang, having made handles, sheaths and big cutters for other people. If I was to make a parang, even in O-1, it would probably get the use that would have gone on the Orford if I wasn't a maker. Then the Orford would end up at home for a lot of the time.
It is the nature of things that if you buy one, you will use it, but if you like having that new item, and using it, and you buy more, your usage is going to wind up divided. Eventually, some are going to see almost no use at all.
I don't think there is a single deep or hidden truth about the buying £300 knives or buyers being too nervous of using them hard. One person might confirm the hypothesis that they bought to collect and wouldn't dream of using the knife because that would ruin its resale...while another might have no objection to using it, but just has so many others in rotation that they don't get to use it, but like how it looks of feels too much to sell it. Someone with a lot of money might buy a £300 because that really isn't much money to them so they have no qualms about using it hard, while another might have little money, but has saved for the best tool they can get that they want to use hard and know they can trust.