Frontier: Elite 2 from 1993 and Frontier: First Encounters (Elite 3) from 1995 did it way before I-War was even a thing, complete with full freeform seamless landing on planets with real celestial mechanics.
I took a look at some game play videos and I'm positively surprised. I seems today's developers mostly just don't care or don't have the required knowledge.
Also considering the lack of exposure and the amount of flack Elite: Dangerous is getting compared to the other space games it's also the gamers who sadly don't care.
Btw here is an interesting interview with David Braben somewhat before the time of Frontier: Elite 2's release.
There is also an impressive universe simulator called Space Engine and they are planning on adding gameplay to it, but it will probably take a long time before it's ready.