1. Why would Sonic even be in a race cart in the first place?
2. Sonic Heroes was teh s**t.
3. Sonic Team is a horrible developer. Seriously, when Sega says that there aren't going to be anymore core Sonic games for a while, they're basically implying that even they admit that Sonic has gone down the crapper.
4. The Mario Kart series is yet another Mario game that is consistently good. Hell, even though there's a ton of them, the Mario sports titles like Mario Tennis, Mario Strikers, and Mario Golf are rather fun to boot. Seriously the only crap Mario games out there are the Mario Party games.