It was a very simplistic market where there was a price floor of ~$5, and prices would randomly go up and down from there (it was not based on buying and selling, it was a simple random walk generator). So it taught me a very simple lesson of patience and delayed gratification, where if I simply bought stuff at 5, and waited a few weeks/months until it went up to 15-25, I could sell with a high profit.
As I acquired more "capital", I could make bigger purchases with bigger payoffs over time, and I made far more buying and selling these stocks than I could ever have performing "labor" (playing the games for points), thus teaching me the second lesson on capital leverage.
I think a few years in, they realized people were doing this, and they added a purchase floor of $15, where you couldn't buy something unless it was $15 or more, which limited my ultra-simple strategy's profitability, but I still kept doing it for a few more years before growing up and moving onto other games.
A final funny anecdote, there was this one stock called BOOM (Boom Boom Boxes), which would very regularly shoot up in value to 100s -> 1000s in price (way beyond everything else which typically topped out in the 10s). And there was this strategy to always buy BOOM when it was cheap, because it would surely multiply like crazy. And one day they announced that BOOM was the first stock to go "bankrupt", resulting in everyone losing a ton of money as it went to 0. Thus teaching me the third lesson about "bubbles".
I'm astounded I remember this much detail from a game I played when I was 10 years old.