I know exactly why and its usually a perfect storm. The same storm that got games like Klonoa 2 but then it came back down to orbit.
Now it can vary on how much of which reason. But it always comes down to these.
"Influencer" creates fake hype
This section can be better known as HIVE MIND. It's been studied almost as long as humans have had brains. In the case of your game. I found that Scott the Woz made a video on Tomodatchi Life less than a week before one of its major spikes in prices. Its usually typically offenders. Angry video game nerd constantly temporarily boosted video game prices with each release. From Godzilla on NES that went from being 7 dollar shovelware to 40 dollar desired game overnight. People like MetalJesusRocks and MattPatt and of course. Scott the Woz. When someone with MILLIONS of eyes hanging on their every word says something. They become like a queen bee. Hive mind. Even if subconciously. Its like when a friend tells you 20x. "Bro this movies epic. This movies dope. Gotta.see this movie" you're gonna eventually start to just NEED to see that movie. Its curioisity. Its also fomo (fear of missing out)
I know this to be the case because its happened to me a lot. And I try to consider myself someone who wont follow the general gaming herd. But I mean were humans. Social animals by default. Even introverts. I heard 20,000 people in my life clammer about astro bot. So guess who opens wallet for astrobot? Lol. I see the youtuber dude with his fancy purple ps5 controller. And I wanted one so bad. So we have an element of that. Of leaders in gaming media. Changing perspective. Driving sales. Thats a gimme. So step 1. Consumerism. Sheep. But thats not enough to drive the price entirely. Next step is....
Demand Overweighs Supply (Sometimes Artificially) and no rerelease (limited options)
Well when IGN, Influencers, even the devs themselves start pushing up demand on a game. Look what got announced on Tomadatchi life? Nintendo openly said last month "we will not be targeting a remake for Nintendo Switch" through questionably offiical channels anyway. Fake or not. Its so what happens is. All those people who are now nostalgic for not only the game. But even 80s kids who just love actual tomadatchis and giga pets. The world just told all 500,000 of them people. Well. If you want it. You gotta get the 3ds one. Their isnt a vita one. Theirs no ps4 port free on ps plus. You got ONE avenue. This happened to (marvel vs capcom 2) then they remade marvel vs capcom 2. And she cooled down in price. They remade paper mario 1000 year down. She halved in price. But theirs one last stap. The game got hyped. Theirs many people who want it but few places to get it. Now the final sequence.
Vultures and Resellers
Their are people who make their actual livings preying on us collectors for sport. Through hitmen and their only goal is to just control our hobby through market manipilation. Be surprised how many intentionally influx demand while holding 40 copies they paid 5 bucks for in 2015. But more importantly. When vultures catch wind that all the 3ds collectors want tomadatchi life. Say theirs 200k people who want it. But only 5k copies in active market to be sold. Then resellers have all the power. They can write 10,000 dollars on one. So if a sucker buys one at 10k dollars. Then it 10k freaking dollars and every other reseller snowballs accordingly. So that may be predatory and scummy. Yes. But almost unavoidable in any market. People want money. Thats part of life. What can be avoided or changed is the final section.
Gamers are consuemrists that eventually cave and overspend and it ruins the market for us who don't
I literally see people on ebay. Bid on auctions. And spend 5 to 25 more dollars on an item than the lowest buy it now price. Just to say they won the auction and outbid someone else. Thats just stupid. I have seen that thousands of times. Not once. Not twice. Thousands lol. I cant even bid in ebay auctions anymore. Go try. You will pay 40 percent over what a game is actually worth because some dude just doesnt care about financial intelligence or his own money. Because its all a joke to him. Now I get it. Rich people exist. But I cant imagine myself rich enough to pay 500 dollars for something another dude is selling for 399 right next to him. Thats just ignorant. But sadly its happening that way.
Well back to the point.
Tomadatchi life is 250 on ebay. Does that mean gamers are held at gunpoint to pay it? Goodness NO. But every sheppard needs a sheep. Every scalper needs a scalp. And simply put. The dumbasses wouldnt pay 40 for it a year ago. But they'll pay 250 today because someone else told them they needed it. Then another person told them it had to be 5x more money. And instead of questioning either of those two people. They blindly say yes yes yes.
And that is consumerism. And its why the hobby is dying a slow sick death like the extinction of the polar bear. Gaming is an ice cap. We are chill as one. And boom. Reseller is UV ray. We lose everything and gain nothing. But they'll be too many people to pay what is asked instead of what its worth.
Other factors not at play here
1. Economy stimuli (covid and presidential stuff)
2. Game Anomoly that suddenly lowers supply (such as burying E.T for atari in giant mass graves lol)
3. Its just rare. (World championships gold cart? Yeah. I mean. It was never gonna be 5 dollars. Some games are just truly rare and price reflects that)
Well OP. Thats the long and the short if it. The game skyrocketed because people started clammering. Resellers noticed and drove price way up. And the final cycle is suckers bought it anyway out of desperation. Its trily a 20 dollar game. All hype is cycle inflicted. Meaning wvery collector is going nuts about it so suddenly others want it. Nobody wanted it. Like rule of rose. (At least that game is rare)