sonic and eggman are kind of like, elemental forces that represent ideas. they won’t change because they can’t change, let alone tell a dynamic story by themselves. instead, their presence acts like walls for other characters to bounce off of. pretty much all of the interesting sonic stories either involve sonic helping someone else through their own arc or him just kinda being along for the ride. and this is why when there’s a story select in a game and sonic has his own story it’s usually kinda just… the most nothing out of all of them? since it’s usually just “eggman’s doing something, we gotta stop him” with little more substance than that, because it’s very hard to give that more substance on its own.
basically my point is sonic needs his stupid friends so they can give his life meaning and vice versa