It’s a bit more than just supply and demand. Just about all retro prices have been on a steady increase consistently over the years because of S&D, especially the lower selling systems and titles, but the big jumps lately are more interesting.
I’d group N64 and GCN in the same categories here, and to a lesser extent, Dreamcast and OG Xbox, too.
Good example of the insanity: Pokemon Gale of Darkness on GC. 2015/16, I would find them pretty regularly. CIB prices were $30-40 back then. So if I found one for $5, $10, $15, it was a good deal. Knowing Pokemon always increases a bit in price, I held onto them to use for trades later. Pre-covid, prices had climbed to maybe $50-60. 1 year later, you can get $200 for a complete copy.
The biggest factor(s) have been the pandemic and age of collectors.
Lockdowns and social distancing gave people a reason to stay home. N64 and GCN have a high number of quality, iconic local MP games too. That’s always driven up prices a bit compared to some other systems.
Couple this with the age of these systems and the age of its fans though. Nostalgia is a hell of a drug.
For someone around 30 yo, the N64 may have been their first system. 25 yo? GCN may bring back a lot of memories as their first experience.
So when millions of 25-34 yos are stuck at home, have more “free” time, and feel that nostalgia pull, it’s going to lead to a interesting retro market.
I’m not complaining, but I feel for those who just want to play some of these games. Dolphin runs very well on an Nvidia Shield if you’re curious…