As a younger collector (25), I think part of it is that a lot of new entrants just aren’t aware of what things went for so when there are a few examples that go at a given rate it sets the perceived market value. For example, I’ve only seen 3 or 4 Berthiers for sale so I bought one with a sanded down stock for 850 which might seem insane to those who have been collecting for a while, but it took me 2 years to find one at all when I had funds so it seemed reasonable to me. If I hadn’t have gone back and read some of the ‘what is it worth’ forums from a few years ago I might have been happy with what I paid!
I see the same thing with some of my friends who are just interested now, who think ANY full stocked enfield is worth about a thousand dollars, whereas to me they’re half that as that was what I found mine for.
Always a mix of reasons why, but I think a lot of it is new entrants to the market. Even things like the recent collection of World War 1 video games I believe had an effect on market value as much as I hate to say it. People like to buy things they’re somewhat familiar with and that exposed a lot of new potential gun owners to firearms they weren’t otherwise familiar with.
In university I also noticed a huge interest in firearms from foreign students in guns. So in the way Long branch Lees are part of Canadian heritage and so go for a premium, guns which are relevant or known in other nations are seeing a bit of a boost as well. For instance, some classmates from China found out I had a Johnson rifle, which is apparently well known there from a popular TV show and so they wanted to pay a fair sum for it, well above what I paid for it.
Add those factors to values that never seem to be going down and you get a situation a bit like the housing market. If people want something, even if it seems a bit high based on going rates it will always just sell for more in the future. May or may not be true, but how many of you who have been doing this for a few decades would have expected to see 2000+ be the going rate for a garand, or 400 dollars be considered a deal on a good sks?