I'll go against the grain, probably unpopularly, but I'll try and outline why.
I have no problem racing without rewinds, I quite manage it in other games like PCars etc, but using rewinds are almost ingrained into the way FM works.
In a game like PCars (or insert other serious driving sim), coming 4th, 10th, 18th, makes no real difference to the game as a whole, progression isn't gated, content isn't gated, races aren't sprints (unless you want them to be), there is no overriding urgency to get to the past 10 AI drivers before the first turn so you as a player can settle down, race properly and focus on the thing that you are here for, the racing, you also qualify which means you generally aren't lumped together with a load of AI that are significantly slower than you are.
In FM you always start in 12th (I think, obviously unless you use a mod car), and the races are usually generally short, combine this with the unbalanced AI which means that the first few places generally sprint away unrealistically (bug I believe), the way the AI don't suffer with the physics as much as the player does (Lotus F1 is a perfect example) and the way that, unless you finish 3rd in career, your progress stops.
All these issues fundamentally make (IMO) rewinds almost necessary for your sanity in FM, and unless some of these issues are corrected, nothing will change.
To stop this, there needs to be qualifying so you aren't starting in the midst of a load of drivers who are many rungs below you on the skill ladder, there also needs to be a massive rethink of the 3rd place requirement, and make coming 8th, 10th, 14th less of a requirement for progression so the player can just enjoy racing rather than have the urgency of having to get into 3rd place to be able to progress.
In short, more focus on the actual motorsport aspect of the game will make it a more rounded game overall and remove many of the frustrations which lead many players to use and abuse the rewind function.
Yep, all good points, and all reasons why Forza continues to be hamstrung by its own basic game framework. Anyone looking for a deeper experience beyond Forza's quick arcade-type fix has to look elsewhere, and that's a real shame. I imagine a lot of players either feel they've wasted their time during a race if they haven't finished in the top three and 'progressed', or simply abuse rewind until they do. The race structure in Forza can force you to focus on the destination at the expense of the journey. The races shouldn't simply be a means to an end - they should be rewarding in their own right no matter where you place. The player shouldn't be made to feel like they've failed if a top-three finish isn't achieved in every race.