I think part of it is that "Wicca" hooks people with this earth-loving, peaceful ideal and misleads people into believing that Christianity is the big meanie that demonized all the wonderful and loving deities of pagan cultures. There is some truth and fact in the idea that Christianity assumed that pagan deities were agents of the devil, but they also worked quite hard to categorize the gods according to their attributes. Norse Thor became a counterpart for Greek Zeus etc and so on. They also catalouged the beliefs, the traditions, the means of worship. So, though they would say Thor was an agent of Satan to deceive the people, they would also highlight the positive worship. Usually chaotic or dark gods were noted as such.
I think another factor is the rather silly belief that the Gods are just happy to be worshipped again and so of course a darker god is goig to be tickled pink and nice to be called upon again. Because they're so dependent on man? Because they're vain? (Well, some are vain
). The Gods do us favors, the gods take time out to interact with us- not the other way around. Sacrifice and offerings were a way to get the gods attention and favor because they are of a higher order than us, because we're dependent on them. They may care, they may have been watching all along, but they aren't cryign in their pillows at night because they've been forgotten. Especially not the darker gods. Then there's also the fact that some don't take the gods seriously. They believe in magic, they believe in the history of paganism, but deep down they don't really believe it. Gods are just tools on a shelf to them and they pull them down when they need one's specific powers or when they liked the story behind them. They flip through a list of gods like it's a menu and pick and chose according to their sense of entitlement or curiousity. And then they don't even have the decency to worship and acknoweldge the god/dess according to her traditions and personality. "I have a special loving relationship with Medusa that no one else understands!" I bet that could make one feel pretty special, which is another perk of changing the gods to suit your needs.
Finally, I think some people identify with the more rebeliious and darker gods because they feel that way in their own lives and wish to be sympathized with and understood as well. Most pagan gods are imperfect. Most have their flaws, their vanities, their distractions and rebellions. But they are on a completely different order than those who are dark, who are dangerous, aggressive, chaotic. It's important to be true to the centuries of wisdom and teachings that accompany the gods, rather than to make them want we want them to be.
Just some thoughts.
I wouldn't say it was added to make it a bad role model.