I hate to say it, but I think SONY / Polyphony gave us a beta version of the game. They said it themselves during February's State of Play presentation that features would be added via updates.
I didn't think much of anything about it at the time, but the ability to start over whenever you want without much of a hassle has always been the most vital part of a game's replay value. To take that away would merit disastrous consequences a couple of years down the line. Call me crazy now, but eventually when people start wanting to do speedruns and "GT7 but I can only use ____" challenges, they're gonna start asking questions. The honeymoon phase for any video game always wears out with time, no matter how good said game is.
Some of us saw this issue within the first few days of release. I'm pretty sure I'm not the only guy who's first time playing a game is mainly getting a feel for the controls, settings, gameplay mechanics, and features, so I know what to expect when starting my official playthrough later. If I had known GT7 would remember all of my experimental choices even if I deleted my save, I would have planned things out from the start before putting the game in for the first time.
However, I don't think that this is a glitch or permanent choice for how the game is played. It's well known by now that the game's riddled with bugs and glitches, some of which can only be worked around by deleting your local save file and downloading it back from the cloud. I believe they intentionally put this mechanic in place as a means of having a temporary workaround for some of the game-breaking glitches present at launch, though I'm not yet sure why they didn't model the cloud save system like in GT Sport, where you could choose between downloading an old save and starting a new game.
Either way, I've elected to not play this game until it's been completed, or at least until I can start a non-experimental playthrough of the game. To pass the time and better prepare myself for an official playthrough, as well as brush some dust off four consoles I haven't touched since buying my PS5, I'll be playing each of the previous games in order of release.