Tornado's post kind of hits the spot. I do think it is easier to understand what he is saying with tangible examples, though. I find when it comes to racing games with licensed cars, a lot of the time they tend to put in cars sometimes on the only basis because they were new at the time, and that being the only factor. They may not necessarily be fast or even performance cars, but they just happened to be new at the time the game was created. I think the ultimate example that speaks this the most is GT2's inclusion of the Dodge Intrepid, a mid-sized sedan that was new at the time and is now generally seen as forgettable by many people. Most telling about these types of cars is video games tend to ignore them once the new factor wears out, note that the poor Intrepid has not made an appearance in a GT game since 2, and I predict it is unlikely it will return. The second most notable example I would say is the the Opels and Vauxhauls that appear in GT5 and GT6, most of them were new back when they first appeared in GT4 but most of them were not notable, the bulk of those car line-ups were compacts or sedans that were new circa 2005 but being just Plane Jane commuter cars are not memorable and look dated in these recent GT games now that the "newness" factor has worn out.
This phenomenon does not only afflict "ordinary" cars, look at most racing games (with licensed cars) from 2000-2002 and you'll notice the 2000 Ford Mustang Cobra R was a staple of many of those titles. Now, outside of Forza and GT (and I would say its existence in the latter franchise is the result of using dated assets rather than PD really caring about the car) it hardly makes a splash in recent video games. I would say the fact that while at the time being the ultimate performance Mustang, better performing variants have come along with time, some of which were not race oriented as the Cobra R and came with more comfort and convenience features. Heck, I would say even certain supercars have been forgotten by video games and the media in general: I remember in the early to mid 2000s the Saleen S7 was trendy and featured in commercials, movies, video games, etc. - now Forza and GT are pretty much the only ones that still pay homage to the car.
I do think the interesting thing about racing games with licensed cars is because of the general trend to try and fit the newest stuff in, they inadvertently become time capsules as time goes on of what was considered "cool" and/or the newest at the time. Take '80s games such as Test Drive 2 with the '80s supercars such as the Countach, F40, and Testarossa. Because of the "new" fad, these cars tend to be squeezed out of recent video games in favor their newer counterparts (example: Need For Speed), and a lot of the times its only games with monster car lists such as Forza and GT that still include them.