It's a kids show, for little girls, and boys are boring, evil, and obstacles for the cute girl characters and should be made out to be evil, idiotic, or serve as a support to the female leads
Spike is at his best when he's there for other characters (Lesson Zero, The Crystalling, Gauntlet of Fire) and every time he's the focus, the writing drops the ball hard (Power Ponies, Spike at Your Service, Princess Spike, etc)