Bob liked having power, regardless of what form it came in.
He liked the power of being an older brother, the privileges that came with it, how Cecil occasionally looked to him for help and protection.
He liked the power of being the host of an educational children's show, and how he succeeded in getting the young audience to hang on his every word, in spite of some calling the Cavalcade of Whimsy's content too advanced for a child to grasp.
In prison, Bob grew to like lifting weights. He could feel his weak muscles gain more power.
He liked the power of being the mayor of a town, and being able to make laws and mostly do what he pleased...or so he thought.
As much as Bob was annoyed by other people's stupidity, he liked the power of being more intelligent than most. Manipulation was easy when there were so many idiots around.
He enjoyed the power of being a performer, leaving the audience in either laughter or awe, perhaps even in tears.
He enjoyed the power of being a father, and being able to mold a new little person into a near-likeness of himself.
There was the power of having a nuclear weapon in his possession, and almost successfully getting TV removed from Springfield.
Bob liked feeling as though he had the power of life and death over others. Perhaps that was why he kept trying to kill, despite a constant lack of success.