Gambling addiction fueled it. There are other extensions that are just as good.
What fueled the beanie baby boom? Reports of big ROI's. Reality? Most people did not make money.
What fueled the shitcoin boom? Reports of big ROI's. Reality? Most people did not make money.
What fueled the meme stock boom? Reports of big ROI's. Reality? Most people did not make money.
What fueled the NFT boom? Reports of big ROI's. Reality? Most people did not make money.
Most people will not make money with .com investments let alone investing in other extensions.
I have seen no proof that the sales reported are fake. However, let's say a scammer starts an extension called .JKL and he wants to get domainers to buy AND hold names in that extension, what would he do?
He would offer low price registrations for names and then find a few of the people that purchased the names that are domainers and REALLY buy the names back using shell companies for big prices. For example, he would go to the person that purchased a name like House.jkl and buy it for 3500, he would do the same with some others and and the sales will be reported and now the gamblers will show up and buy names.
All he has to do is to keep making those investments that seem big but he is making it all back from registrations and renewals. Plus, the owner of the extension is holding some premiums and it drives their price up.
The domainers that are making the sales are not in on it and the only people that would know would be the person behind the extension.
This is how market manipulation has worked in other industries too.
The only clue might be that almost all the big sales would have nothing developed on them. Even that is not so much proof because many big .com sales remain undeveloped but in many cases you can trace the buyer a lot easier.
In the case of XYZ and IO for example, you do have real companies using them. Very small market but they do exist.
I remember when a well known domain auction house was caught in bid rigging, I remember the fraud in other markets, I am always skeptical but believe in innocent until proven guilty.