This is not a hard concept to understand. Example:
Once upon a time they were selling for $700+ each fish for all the reasons you mentioned. There was a ban on exporting them. Their egg clutches are small anywhere from 6-15 in most cases and there weren't many breeders that had mass quantities of breeders to produce enough to meet the demand. Also many breeders were trying to sell only males to prohibit anyone else from breeding. Again as you mentioned this fish takes some work to breed, water quality has to be right, it takes 3-4 years to reach sexual maturity, seasonal changes/food/habitat etc etc...it's not a fish that just anyone with no work ethic or lack of time can throw in a tank and breed. Many many factors to consider in the price of this specific fish.
To my knowledge all Corydoras catfish are sexually mature and capable of breeding at 2 years of age and many can breed when 1 year old. The females also produce more than 6-15 eggs and many females shed 50+ eggs per spawning.
Companies like Aquarium Glaser know how to breed fish and Corydoras aren't hard to breed. The fish are well fed and looked after. When they are in breeding condition a group of 6-10 fish are put in an aquarium and a massive water change is done with cold water. The next day the fish have bred. It's not rocket science.
This is capitalism 101....if the supply is low and the demand is high prices are also going to be high. Anyone who sold these fish for less to the general consumer 20 years ago would have been a legit fool. If you think otherwise then you're a fool and have little understanding of modern economics.
I know how capitalism and modern economics work and it's one of the reasons we have poverty in the world and 1/4 of the people on the planet are overweight and suffering from type 1 or 2 diabetes or pre-diabetes, while the remaining people starve to death.
Modern economics where the rich can afford medical care, dental care, education and all the food they want, including enough to throw some away, but the poor don't even have electricity to run a light bulb at night or a decent meal each day.
A lot of crime is caused by modern economics. Poor people want basic things like a television, food, whatever, and they can't afford it so they commit crimes. They are often treated as outcasts and ignored by governments. Many poor people have higher rates of incarceration compared to rich people due to lack of education and lack of money to afford the best lawyers to get them out of trouble when they get into it.
A lot of poor women get abused and live in crappy relationships because they aren't educated and are expected to marry at the age of 12. This is modern economics at work.
Modern economics where first world countries like the USA, UK, Germany, Australia and all the other countries with modern conveniences and cars are destroying the planet simply because they have money and want more money. Meanwhile the poor people are dying on the street because fossil fuel powered machines that are used by richer people have screwed up the planet and caused the temperature to rise, the rainfall to either increase or decrease in the area, and major changes to the environment and weather patterns to occur.
Modern economics where companies can make and sell carcinogenic chemicals for agriculture and those chemicals are on our food and in our waterways. And governments allow them to sell those chemicals instead of banning them. Why, maybe the odd deep pocket handshake with political allies?
Modern economics causes war, famine, and death to the poor. The average and poor person on this planet are still slaves to rich people. The only difference is in most cases, they get to go home at the end of the day and live with their family when not working for the rich people. They also don't get whipped in the richer countries but do in poorer countries.
Modern economics where rich people clear land and destroy habitat that animals live in and this catfish is an example of that. The land was in danger of being cleared for farming and it got protected but the fish is still threatened in the wild, as are all wild animals, birds, plants, insects and reptiles. All because of modern economics. We must make as much money as possible by raping the Earth.
Modern economics where gun clubs and billionaire families can dictate government policy. Where companies have more money and power than governments and are above the law. One of those people is currently running for political office and he committed treason but has never been charged for it.
Modern economics where certain western governments interfere with other poorer countries and help put certain people into power so the western country can get resources from that country at a discounted rate. These governments are also regularly involved in wars caused by their interference. Most wars around the world are caused by modern economics and people wanting power and resources.
Modern economics whereby everyone wants more and more money. You can't have infinite exponential growth in anything because eventually you run out of resources and the system collapses. Most western countries are in a global recession currently and this is not the first time. It happens regularly because of capitalism and modern economics. About the only thing holding up economies currently is their war footing, manufacturing, selling, supplying weapons to other countries. Or in the case of Australia, our government decided to bring in millions of immigrants to artificially buffer the economy so we didn't go into a recession. The average person here is in a recession but on paper the immigrants stopped the economy going into recession. The immigrants forced hundreds of thousands of people onto the streets and they are now homeless, and it pushed up the price of housing here. So now we need more money just to pay the rent to the rich people who continue increasing the price of rent just because they can. Covid19 caused the price of everything to go up as well.
Modern economics has destroyed this planet and whilst some people might think that is fine, I don't. There will be no equality among people until everyone has the same rights, education, living standards, food and the right to life. There will be no equality until the poor get the same special treatment as the super rich, and the rich are held accountable for their actions when they break the law, destroy habitat that is home to other species, encourage wars, or generally ruin the planet because they don't care about the ground they live on. They only care about how much money they can make this financial year. And that is what's wrong with modern economics.