It's been years now, but I used to be involved in the trading market for Team Fortress 2. There were people who did TF2 trading as a full-time job, exploiting arbitrage between markets and holding items that were expected to increase in value (and sometimes using bots to farm items).
The Mann vs. Machine update in 2012 added a new game mode that would give players loot as a reward for completing missions. Players who didn't care about the trading market (i.e. the vast majority) would look up trading sites after a gaming session to offload their stuff fast without caring much about the value. People who described themselves as "quickbuyers" would aim for the people who wanted quick and simple transactions and then sell the item elsewhere for a markup. I did this for a while and averaged $5-10 of profit per day, usually 20-30 cents per transaction. Someone treating it as a full-time job could probably have made a lot more, like $20+ per day.
That was pretty good money if you a) were a kid with no living expenses, or b) lived in a developing country where the money went farther. I was in group A. Any time I wanted to buy a Steam game, I'd put up my quickbuyer listing on the trading sites and save up the money. But I suspected at the time that most people in the scene were in group B. If I were Valve I'd struggle to pull the trigger on a major change to the in-game economy knowing that it would affect the livelihood of a nontrivial number of people in countries like Venezuela, and maybe that's the reason they seem to have hesitated for so long.