(flight sim fans should not read, this is for EA execs & producers)
In short, around the time that Falcon 3 came out, I think the success of that resulted in large shift toward the simulation/realism aspect (though I suspect most developers interested in flight were always driven toward more realism). This is certainly interesting goal but it's quite shocking how what I thought back in early 90's as being one of the most popular computer game genres turned out to nearly die and you could argue it did, from mass market perspective. Lack of joysticks and such are often cited reason. My argument is that the kind of flight games that I envisioned never even arrived! Battlefield 1942 Desert Combat modification has been the closest to what I thought about back when all the true mass market flight games were around: Strike Commander, F15 II, F19. (and bunch of WW1/2 stuff I'm not into)
I've now been playing Strike Commander again in dosbox and thinking, why is this game still so good - of course it's nothing to do with *realistic simulation* - as any game developer worth the title should realize, games aren't about realistic simulation but more often about providing fun - awesome experience, one you could not have in the real world. That's why they're games and not simulators. The simulator niche market could not even keep the fabled "Flight Simulator" alive.
The whole joystick argument is quite non-sensical as well. I can fly Strike Commander and BF1942: DC just fine with keyboard, it's no different from driving cars in Trackmania with keyboard, infact it's much much easier as flying doesn't require such level of precision timing. Trackmania has tons of players and is as far from realistic driving as you can get, yet it's extremely immersive and feels like you're really driving.
So what's the whole argument about then? Looking at what makes SC and Battlefield fun to fly in: It seems to all come down to a scale that has been adjusted for 1) short distance/time to action 2) the maximum flying altitudes and terrain height has been scaled to make for most compelling game experience: most of the time, whether you want or not you are actually flying slow and close to the terrain, making the terrain play a role. Helicopters are much better suited from immersion perspective to this and fast jets are worst suited. But as action-flight player I have found it doesn't really break the immersion of flight even if the "jets" are scaled such that the player seems to always be close to alps height mountains and seemingly fly in canyons with large planes. 3) the way the planes react to control and the sound are big deal as well - notice the special effects during flight in Strike Commander, likely unrealistic (?) but add lot of immersion.
The ideal action flight game scale for jets seems to be something between SC and BF1942.
How to reconcile the scale issues and have "jet-like" vehicles in a game? The answer is, keep the scale at Battlefield level, maybe making the maps slightly larger, ceiling altitude slightly more, ~100 players on the same map on average. And instead of traditional jets, have armed UAVs controllable by players in addition to helicopters for troop transport. The UAVs can be smaller and more limited in armament thus allowing larger numbers of players in them without making life as infantry or tank player too frustrating. (of course some multiplayer maps need to have bombers for some epic carpet bombing of infantry it wouldn't be a proper flight game otherwise)
Why were F15 II and F19 special flight "sims". They certainly weren't the first flight sim I played so that cannot be biasing my memory. This is much more challenging to answer but being a very visuals oriented person I believe the answer is that these games still look very compelling even today. Completely unrealistic visuals but they still manage to convey strong charm and mystery, created mostly by careful palette selection where gray fog does not dominate/exist. This is why GDC presentation of Another World spent lot of time talking about palette - especially important during first impressions such as screenshots and demos or first minutes. Doing palettes right with 3D is much more challenging. Notable about these two games is the software rendered- pseudo-3D visuals forced by limited color selection, so a lot of the terrain and sky always have the ideal colors and no grey/green/brown-foggy appearance typical of modern flight simulators. Again Battlefield even when it is 3D managed avoided this problem by virtue of the planes mostly flying very low altitude - the visuals were dominated by the striking terrain palette.
Now gamers will undoubtedly think I'm mad talking so much about such "irrelevant" aspects of games that don't relate to game play, but this was not for you. I've read review sites statistics and people still look screenshots before reading reviews. Palettes, visuals, first impression matter *very much*. If those things aren't right don't expect instant sale even for otherwise great game.
edit: Unlike you might think I'm not hyped about Battlefield 3 since I suspect it has the ridiculously bad flight controls/feel from BF Vietnam & BF2. The BF1942 DC *mod* had the supreme control system - about as much fun as Trackmania. The DC mod felt a lot like Strike Commander and the helicopters were super fun to fly on keyboard - since they fell from the sky like a rock if you weren't really trying to fly it constantly! - unrealistic yes but fun and very challenging!