A lot of people remember Error 37, because this was the first time a Diablo game could only be played online and their servers were full.
The devs wanted to prevent item duping as well as players selling items on Ebay. Unfortunately, players are still selling items today.
There was a wide range of players who played: kids who didn't have money but a lot of time, and adults who didn't have much time but a lot of money.
The Real Money Auction House allowed players who would rather trade their money than their time to get good gear in order to equip their characters.
But the game became Play2Earn when players played it 8 hours a day, flipping items for real money. It became their job.
When a game becomes like a job, it's no longer fun and players move on. We've already transitioned from Play2Earn to Play&Earn- fun first, earn second.