So now Sega has a winning formula where there's no story, all the friends are there but don't do anything, and you just run fast as Sonic, except that winning formula burnt out after the beloved Generations and both Lost World and Forces went over like lead balloons, and the natural consequence of leaving the friends out is that they also get devalued as characters and don't really matter to the franchise anymore. The longer answer gets into a discussion about what the franchise itself should be about and its reputation back in the 00s where every game leading up to Sonic Unleashed had loud conversations to the effect of 'I hate these characters, I just want to play as Sonic and run fast', whereupon Colors released, stripped out the Werehog gameplay (and with it several hours of the runtime), and was the Fandom Agreed First Good 3D Sonic game. The quick answer is that the friends are usually the face of experimental gameplay styles that are pretty hit or miss and get away from playing as Sonic, who's the star of the show but whose zoomfast platforming demands levels that be completely in a few minutes.

Sonic adventure 3