Not really agree on all your points, yes it has already been done, and it's done better on PC, but considering console market theses are 2 more serious propositions, well IMO, and not so much equivalent on the market yet
Again I was talking for console audience
They are new on the market, they need time, again I'm not telling it's a perfect product, just saying theses have good foundation and they deserve some time to deliver their complète vision
Project cars 1 and 2, Assetto Corsa, Assetto Corsa Competizione, even Forza Motorsport and Gran Turismo 7 to slightly lesser extents, all do most of what Rennsport and PMR do or claim to do, better. With the sole exception of modding, which as Scaff has already said above, as well as me, really hasn't been utilised to enough of a degree to be a genuine selling point or reason to buy PMR on console.
There may be less choice on console and whilst PMR and Rennsport will, and no doubt have, sold better on console because of this, it doesn't make them the de facto choice when other games have already done what they offer, better.
The choices on PC simply resigns them to the bargain bin of the sim world and, if we're being honest, Assetto Corsa and it's modding capability could have done that single handedly. Add in LMU, R3E, AMS2, rFactor 2 and iRacing, plus a historic library of sim racing classics.
GTPlanet has always had Gran Turismo as it's primary focus (hence the GT), with select other titles featuring should they demand enough of a following to do so, Forza being the biggest series to get regular coverage. PMR and Rennsport are far from the only sims to lack coverage, LMU, iRacing, AMS2 rarely/never feature. There simply isn't enough value in covering them here.