I just think there was way less competition. No warthunder, world of tanks/planes/ships, Il2's
I don't think that's it.
Warthunder and World of Warplanes started 5 years after 2007.
What was causing the upward trend of 2000-2007?
The demise of Air Warrior might have added players to AH. Air Warrior ended in December, 2001. But there was already a strong uptrend in AH from 2000 to 2001. Also, it would seem odd that a game that ended in 2001 would still be adding more players each year all the way out to 2007 to AH.
Just that Aces High was new? I don't think it was that. There were Air Warrior, Warbirds, and Fighter Ace, and even Il-2 Sturmovik, so the genre was not brand new and not without competition.
What changed in 2007-2008?
There was an economic crash. But there was an economic crash in 2000 as well.
There was one dynamic in 2000-2007, and a switch flipped giving another dynamic in 2008+. But what was that switch precisely in 2007/2008, and what was the driving dynamic 2000-2007?