This is probably deeper than the subject you were expecting.

An observation:

When playing a morally retarded RPG (an RPG with a moral system) I generally find playing as an evil character far easier. It's easier to raise the evil moral stat bar than it is the good, and thus you are granted access to the evil bonuses sooner than the good. The evil bonuses are often more offensive in nature than the good bonuses meaning that it's easier to trawl through through enemies.

Due to this percieved lack of challenge despite the joy in torturing, murdering, and generally being a bastard, there is less to enjoy when playing evil. And it's usually the "wrong" ending obviously.

BULLET POINTS:

1. I am naturally evil and thus playing as an evil character is easy.

2. Conversely: I am naturally good and thus do not enjoy torturing, murdering, pillaging as much as I would like to think, though this does not apply to games like GTA.

3. I often play the evil way on a second playthrough because the good ending is almost always literally that.  On a second playthrough I will obviously have more knowledge of the game.

4. Being good is inherently harder than being evil.

5. Given the less effort put into the evil side of the story, perhaps the same applies to the gameplay and evil perks? This may contradict the point about it being easier, but if it's too easy then it's a balancing issue.