There have been some good replies already.
Knowing a few people involved in development of past and present sim-racing titles, what I'm very sure is that
decisions around development today have a lot more to do with money, and less about what the developers really want to create or innovate.
Developing sim-racing games with bigger detail (and newer tech) today is more expensive than before, especially since most developer-houses in this genre are self-financed (no more big companies funding from behind).
We had a time when specializing a game-title for specific racing-series was the first step.
Instead, we now have game-titles composed of mish-mash of cars+tracks that, more often than not, are more appropriate for a track-day and hotlapping (driving) simulator, than for a propper racing simulation.
You can't accommodate different automotive disciplines and classes/categories in one game, then hype about the highest levels of racing details for all, because that's impossible. Something has to give (obviously) and I think the lack (or loss) of features became the first "sacrifice" decision by committee.
The budgets, user statistics, sales results, popularity status in the community (etc) became ever more important.
And I think this is the number one issue, the root of the problem.
Also, the lack of vision and innovation among simracing developers today is shocking.
I facepalm everytime I read/hear a developer embarassing himself by saying
"No, we will not have day-night cycles, or dynamic weather (or this, and that, etc) because most will barely give it attention".
This has been a constant, and it's moronic.
With that line of thought (typical commercial assumptions), some of the best sim-racing titles wouldn't have existed.
For example,
GPL. This is a paradoxical game in that, in its day, the ROI was pathetic (it was a commercial failure). Yet,
GPL was perhaps the biggest jump-starter of a whole movement in a growing and changing community of gamers. It is the most iconic and inspirational sim-racing game of all time.
Roll back to that time and, I'm sure, some of you will remember it. Not just the game itself, but the years following its release. The amazing high standards and caliber of modding around it. The leagues, the gentlemen-(sim)racers, the levels of maturity involved, perhaps unseen before (or since, some would argue).
The point is,
GPL was the sim-racing game its developers really wanted to make - within their capabilities and budget, I'm sure.
And that's when magic is done.
I could mention others, such as the original
GTR by Simbin, following the dream involved in that huge modding project by SBDT just a few years before, called
GTR2002, back when they were talented modders and not the popular developers they would become.
Eleven years later, its sequel (
GTR2) is still considered the most complete sim-racing game!
And also
GT-Legends. You see, Ian Bell has been criticized in recent times (and
PCars has been somewhat controversial among sim-racers) but, back then, he knew very well what tickled
GPL users (which he and part of the Blimey/Simbin crew once were too), and knew what was missing in the sim-racing scene.
Perhaps it was a risk then but, twelve years later, we all drool just thinking about a sequel to
GT-Legends made with more modern, higher standards.
And we still talk about these older game-titles today with fondness.
There are reasons for it. Nostalgia only goes so far.
Newer simulations missing important features for the context, which are found in much older ones, is inexcusable (IMO).
There are other things. For example, we have already reached tremendous levels of graphical realism. When will the audio follow suit?
(sounds are still the aspect which developers care the least)