I still remember dealing in the seventies with the likes of Fishwicks, (the original) Jessops of Leicester and the large Eurofoto Centre between West Drayton and Uxbridge. Fishwicks (or was it Jessops, memory fails me) had a very thick paper catalogue; almost as thick as Exchange and Mart and Amateur Photographer were, back in the day. It was also a time when you could buy a camera and it still be a current model five years later.
Fast forward to now when, if you are not quick enough, the camera you bought yesterday has been superseded by lunchtime today and the corresponding value, second-hand, has dropped off a cliff (not so much the higher end of the big manufacturers though).
New developments are getting thinner on the ground now IMHO. Take the iPhone -- I believe we are now on iPhone14? -- what can they do to make it as desirable as the older ones were in their time? Everything has been done; more memory, better batteries, more pixels in tiny sensors, but none of it is going to be enough for people to dispose of their perfectly-capable earlier models in large quantities. I always used to look with greedy eyes at new phones but I've had my LG now for five years and it is just as big, has just as much memory and the battery lasts just as long as the latest Samsung.
Mirrorless cameras seem to be bucking the trend for declining sales perhaps. although quite why this should be I don't know. As many have said, it is hard and of dubious value, to be dumping onto the second-hand market thousands of pounds of, say, Nikon FX cameras and lenses to reinvest in a completely different system (yes, I know the older lenses can be adapted, but it's just not the same is it?).
These days I try to invest more into small artisan establishments as the prices are not too different if you take in the quality. I have just bought a pocket knife from Michel May Knives, made with Damascus steel and an oak handle it cost £140, but the quality is out of this world (with a stainless steel blade the knife is under £90). I have three 'quality' knives, bought over the years, which cost at the most thirty quid, but they just don't hold an edge and the blades wobble a bit. I still believe you largely get what you pay for.
Sorry, this has become an essay, I'll stop now.