Well actually they do. During the development of both PCars 1 and 2 this has been talked about. The community pretty much unanimously said no.
The feature does not promote people to actually learn in most instances since many people will continue to use it instead of pushing through and getting better. I'm a believer that whatever you do in life you should always strive to improve and not just take the easy option out just because it happens to exist. The easy option is rarely the better option in the long term. Clearly there are some people who disagree with me but that's fine, rewind has not infected every single racing game out there and there are still quite a few developers who believe there are better ways to learn than to rely on rewind.
And it's worth noting, the sim racing community by and large are very welcoming to new players and are more than happy to help where possible provided said new player wants to learn. In many cases, if the player is not willing to learn, goes to a discussion forum of a game that doesn't have rewind and just complains about the game not having rewind rather than saying "this is where I'm at, how do I get better?", then yes you will get the cold shoulder.
Citing online discussions is a very loaded sample. Sure, when you surround yourself with likeminded people, then they all "unanimously" vote no to something like a racing. It would seem that the developers actually didn't take that opinion on board though, if the final game contained one anyway, despite the apparent unanimous call to not include one. They must realise that the casual racer that would vote "yes" is likely to not be on a community board for a game currently in development... shocking thought, I know.
As for it not promoting people to learn... I find that stance to typically be held by those themselves had learnt without the help of one. I've mentioned before, that I previously hated Gran Turismo, coming from games like Daytona USA and Sega Rally, as I had no idea what I was doing, and why I was failing to make turns successfully. I wasn't until I played F355 Challenge, which happened to be the first racing game I ever encountered with a dynamic racing line, where I finally learned what I needed to in order to play the game successfully. This then transferred onto Gran Turismo 4, and now racing games are one of my favourite genres. Sure, there
will be people that never bother to better themselves, and grow beyond their reliance of these features,,, but this holds true even when the assistance
isn't given. I've seen people ride the wall in Three Seven Speedway for YEARS, never learning the game's drift mechanics, and god help you if you find yourself anywhere near them as they do so. There are people that have played Street Fighter since Street Fighter 2, and are still flowchart Ken. These people will fuck up your race
regardless. They were doing so in the original MotoGP and Project Gotham 2 on Xbox, where doing so to all the AI in Gran Turismo 2, and would still be doing it online in Forza Motorsport 6.
The only thing that prevents this happening, is when a game is rendered so inaccessible at its core, that they stop playing entirely... which...
This is pretty much my stance on it. It might come off as "elitist" in some people's minds but I simply don't care, my time is too valuable. If I want to race online then I should be able to have a decent experience, not have to fight through a bunch of people who don't have a clue what they are doing, that's a waste of my time. From experience, it is much more likely you will be able to find a decent race against randoms in a game that doesn't have rewind (assetto corsa, PCars, GT, race room experience) vs games that do have it (Forza Motorsport/horizon, F1 games).
So if that's the case then the games with rewind need to do better and find a way to separate players based on skill level.
... basically seems to be what you want. To just have these people not play online (or that game at all) instead.
As you mention in your last sentence. If Forza has a problem with stuff like this, then it's a matchmaking problem, not one of the feature existing at all. A poor player is just more likely to have the confidence to play online in Forza, they should just be placed far away from players proven not to crash.