Flight simulators have always kinda followed this pattern though (short of the "free" base game) - DCS just figured out that the genre enthusiasts were likely to buy a couple of pieces of DLC anyway and they would come out ahead giving the game away for free.
Look at the original king, Microsoft Flight simulator
The game is 12 years old now and has regular DLC releases, of which total almost $4,500 if you want them all. Train simulator on Steam has always been pretty similar, giving away their base game in cheap bundles for years knowing that people will buy a couple of pieces of DLC to make up the difference.