I think there is a pretty large segment of the customerbase that are not flight sim fans.
What? You might say.
I don't even like flight sims. However I still own almost every module except for the Hawk, CC101 because they are substandard products. And I am still very sorry about the halfbaked Mirage I bought.
I even bought the Albatros, and all ww2 planes.
Why? Not because I like flightsims. Because I like playing with a complex machine. And that is why DCS provides. A highly interactive game where you get to handle a complex aircraft.
And if one breaks down each dcs module to the level of cockpit complexity or clickable switches, then the Mi8, Mig21, and the Viggen are very fun to play. Because of the complexity it provides.
The ww2 planes however are all the same unless you want to geek out on aerodynamics.
And for the non-flight-sim customer, a viggen next to a spitfire will make the spitfire look very boring, simply for the lack of stuff to click.