I don't think it's a knee-jerk reaction. Instead, it's been 2-4 years of tons of WW2 games of pressure on that knee, and now the knee has reacted.
Anyway, flight sims will focus on WW2 games for a looooong time coming. Although WW2 and it's aviation technology was only around for about 7 years, all the other years in the 20th century feature either planes that are TOO SLOW.... or planes that are too fast and feature beyond-visual-range missile combat. So there's a good reason for a WW2 flight sim again... cuz that's really the only kind of flight sim that can sell. Jet sims have a billion buttons and MFD readouts to keep track of. I loved being in my F-22 in Total Air War, punching away at different MFD functions and such. But the learning curve was steep. WW2 sim curve? Grab a joystick and pull the trigger. :-p Not to mention that WW2 sims are the only sims that have a reason to put up hundreds of bombers in the air for you to gape at. Every modern sim, you see a pair of planes and that's about it.
Personally, I wanna see someone breathe new life into the modern sim genre by NOT being realistic, but taking what is cool about modern sims, and modifying it into some sorta sci-fi alternate reality world. You know, kinda like Macross Zero's take on modern jets