I don't know the exact date that 15$ subs became a thing. I believe it was around 2000. It definitely was by 2003. Check this out though:Inflation Calculator
Put in the year you played your first 15 and the year you played your first 15$ sub game and hit "Calculate".
Based on my estimation of 2000, a 15$ sub should now cost people 21$. Yet subscription prices have not increased whatsoever. People just want to go back to the good old days of 15$ subs but it's a lot like people who want to go back to the good old days of five cent coffee. It's been 16 years. We went through a major recession during that time period. 15$ doesn't pay the bills anymore.
No consumers have ever shown any indication of being tolerant to them jacking up the prices though. Any MMO that did would be massacred by public opinion as "greedy money grabbers." So they gave us cash shops instead. That's on us.