I don't know what happened but 15 bucks a month won't get you much these days...
Back in the day it seems everything was subscription based. I remember playing Everquest, AH, World of Warcraft etc and they were all monthly subscriptions, but I don't think that's the norm anymore.
I think the revenue model has changed overall with most games offering something for free or for a 1 time purchase and/or in game transactions. I know you can fly some stuff in DCS for free, you can fly lots of stuff in WT for free, and you can get into IL for less then a one time purchase of less then $20.
I think most younger people are gonna go for the games with the FTP stuff or one time purchase. For example, I have 3 kids that I can play Roblox, Minecraft, World of Warcraft, War Thunder, and IL2 with at $0 cost for me per month. It's because all of them offer some level of FTP or one time purchase. If we were to play AH3 together that would be $60 a month. Sure, it's on $2 a day but it's also $720 per year which is more then I spend on all the other games combined in a year.