It's because during GT Sport, KudosPrime had all the points info available for each player.
After each race, we could see exactly how many points we gained or lost. People just did the math to figure out PD's formula.
We've not seen any evidence that the scoring has changed.
In GT7, PD made efforts to better hide our stats from us. They never wanted us to have that info, but some computer geniuses figured out how pull that data from their site. If anyone has figured out how to get the individual driver stats from GT7 (possibly
@Nenkai, or the Hungarians that run the GTSH-Rank site), they aren't sharing it like
@Milouse did with his KudosPrime site.