Let's flip it round a bit, GT5 and 6 were more ambitious yes, but also the worst received of the main series games by critics and the most criticised among fans. Typically in the industry you wouldn't want to build upon multiple perceived failures.
I think there's a very good argument to be made that the only reason 5/6 received more criticism from fans was there was more people playing/engaged in the games to complain in the first place. That was still in the GT console domination era, GT7 is not.
The criticism that 6 received was almost entirely that it was a PS3 exclusive launched at the console's life, that it seemed like somewhat of an asset-flip, and the standard cars. There were complaints of the AI, but that's an omnipresent complaint in the series. All issues that deserve criticism, but the core of the game, ie the content, didn't get a lot of hate from players that I can remember from my old GTP account. GT7 seems to have the opposite issue: it's cross-gen so many more people can take part, the cars that we do have are mostly well done, but there is a gaping hole where the core of the game SHOULD be. People will play a game with issues if the content is decent and plentiful, (Dragon's Dogma, Kingdom Come: Deliverance, all of the Gothic series, etc, etc) but they completely walk away from a polished game with nothing to do after 30hr. (The latest Battlefield, GT7, MMO's like New World, etc) It's not until you get into Cyberpunk: 2077 levels of jank will people abandon it in spite of the content on offer.
GT7 sold well, but if my calculations are correct only around 400k took part in the Time Trial, in a game that's less than a year old where there were 10 days to submit a run. I don't see a way to quantify the participants in the race at Spa/Willow, etc, so the Willow TT is imperfect but all I can find. So if one had any interest in engaging with the Anniversary content there was more than enough time. How many copies were sold? 6-7mil? Thought I'd seen that somewhere but maybe it was just unconfirmed speculation.
Even if its 4mil, PD's only retained 1/10th of the player base, and I'm sure a great many of them came back after a long hiatus like myself (I strongly believe its much higher than that given it was keeping pace with Elden Ring in March/April/May, which sold 16+ million to date, so I'd guess around 5-6mil if one wants to assume each of the three major platforms gets equal shares of sales)
As for critic scores, well, who cares... This game received glowing reviews at launch, then a massive backlash from many of the YT/alt-media critics once people got deep enough into the game to see it was a Potemkin Village seemingly designed to get high critic scores. So I wouldn't weight critic scores very heavily given all the content was front-loaded in a way that would make critics think everything is polished and intact.
I'm not saying you're wrong about not building off of the GT5/6 template due to the issues they had, just playing devil's advocate as to why the amount of player criticism and quality of said criticism may be an "apples to oranges" comparison.