First up the majority of them guys will go to World of Planes, a lot of people equate realism or a realistic flight model to how a game looks, take IL2 for an example I'd describe it as an immersion game not a combat simulator. World of Planes looks pretty but not real in the same way IL2 does, it looks like your watching a painting of the scene, even watching the cgi in red tails trailers it also looks like a painting.
A lot of these people simply won't want to wait maybe a year or 2 or more to get reasonably compotent in a game. They want some success within at least the first few hours. In Aces High that won't happen.
http://www.youtube.com/watch?v=SBHQMizctgYFunny reading up on this people are whining about how they hope this game will take skill rather than upgrades, you'd have to wonder why they didn't just go play Aces High, probably because they are full of it
I was thinking back to the first time I played this game I actually logged off after an hour or so and forgot about it for about 4-5 weeks when I came back my trial had expired but there was still H2H free 8 player.
Gradually after about 10 or so new ids over the course of maybe 2 years I was hooked, when H2H went I found I had to subscribe to get my fix. Point being it was the fact that H2H was free that got me hooked, if I had been straight up asked for payment I would have forgotten all about Aces High and deleted it.
I'm working from memory here but I think H2H would have went in 2007 sometime?? I remember looking at one of Lusche's pie charts the peak of players was in 2008. Just saying free H2H might be the reason the numbers have declined.