It's an unfair, bias'd complaint. Most of the characters that SEGA adds last for a single game and are hardly ever seen again. The main and stabled cast of characters is Sonic, Tails, Knuckles, Amy, Robotnik, Shadow, Rouge, Omega, Silver, Blaze, Cream & Cheese, Marine, Big & Froggy, the Chaotix, the Babylon Rogues, and probably Mighty & Ray if they ever return. And many of the characters mentioned don't appear as much as each other. The rest of the characters added just last for a single game. And usually never to be seen again. The next characters to added in the main cast will most likely be for the 20th Anniversary.
And look at Mario's characters. Last I check'd, there was over 46 and Sonic has over 26.
This is all just unfair biasm.