I understand the writer's has a big affection for fantasy or fictional track but let's be honest, they are not "important" at all.
In Gran Turismo 6 I actually enjoyed the fictional tracks the most (like Mid-field raceway or Eiger), I think PD does in fact understand the needed fluidity of a racing circuit the best. In Driveclub I think the majority of circuits are quite fun as well. But it stops there. In Forza Motorsport 6 I really like the looks of tracks like Prague and Rio but let's be honest, as a racing track they are pretty poor, it's at best a visual spectacle of <insert your annual Turn 10 city focus here> and nothing more. Going forward to Project CARS I really like the looks of California Highway or Azure Coast but they are nothing spectacular to drive on. If you want a fictional point-to-point coarse I think PD's Sierra circuit still is best. Then Assetto Corsa's fictional tracks are weak too, Black Cat County is really dull and the more recent Scotland highway track is so overfilled with sponsor advertising boards it's really annoying to drive on (they did a better job than with BCC though).
For me the thrill and fun of racing on a circuit in a sim racing game is to have my driving/racing experience as authentic as it can be. Rig setup, a realistic car (no Vision GT, SMS-R or other fantasy cars either!), a realistic handling model, a realistic track and realistic graphics, sound and weather effects. For me what sim racing is all about is to come as close as possible to what the real deal in a real racing car is. And it's just thrilling for example to race a Group C at the long Mulsanne straight (pre 1990 layout without chicanes) knowing that this is what actually happened in real life as well. And it's not just a long stretch of road, it's a piece of history. The same goes for classic formula cars on those historic versions of Silverstone, Hockenheim or even Rouen-Les-Essarts in Project Cars. Or a modern GT3, F1, LMP1/2/3 on any circuit they also race on in real life. NASCAR on ovals, V8 supercars on Mount Panorama, rally cars on real life stages as in Dirt Rally, Rallycross on real life RX ciruits, Indycar on US tracks, ... it's just incredably fun to recreate real life races in sims as well, it adds an extra dimension of realism that a fantasy track (or car) can never do.
Fantasy tracks IMO are good for arcade games, the Need for Speeds and the Forza Horizons of this racing world. Granted sims are by far my favorite genre but I do enjoy an arcade racer as well and there the fantasy tracks are fine since the game as a whole is not as serious either.