its really hard to make something like that fun. The real world economy is driven on asymmetrical inefficiencies and lack of information, things that wikis and game balance pretty much destroy.

It's only fun to make money on say world of warcraft because most people aren't also doing that. (but instead buy your goods and use them for something essentially unproductive in economy-terms) Even then it can feel pretty stupid given the amount of arbitrage bots people have set up, you have to focus on very niche opportunities or oversights by those arbitrage bots. Kinda like the real economy