The Sonic fanbase is naturally biased towards it. I played the game. I really don't understand why anyone would willingly buy and play that game. I tried it with the purpose of determining whether I might want to buy it, and it was one of the worst racing games I've played in years. Pit stops? Abysmal physics? Sections of the track where I rotate the stick for no good reason? I went from "This game might be worth a purchase" to "I'm never playing this again" in 30 minutes, and that's a pretty severe reaction if you ask me. I can't be the only one that absolutely hated it, and apparently, the game reviewers agree with me.
I think it's now boiled down to two camps of Sonic fans: Those who blindly love every Sonic game that comes out, and those who realized that the series is in the toilet and somehow, SEGA takes a good idea (Sonic racing game) and drags it into the mud every time. You obviously love whatever SEGA releases, and honestly, I don't have a problem with that. If you enjoy it, who am I to tell you to stop having fun. However, a large amount of people don't enjoy it, namely "anyone who isn't a Sonic fan", and that's why it gets such low scores. Game reviews are always going to be based on opinion, and public opinion is generally pretty negative.