Asklemmy

I don't mean to be a bit obvious but I really think of all the insightful analysis you might get it really boils down to "he's a cartoon character" both literally and metaphorically.

When he's evil, it's funny. His evil plans are... well... cartoonish. He tried to block out the sun, he built a factory that uses the plastic from beverage packaging to deliberately snare sealife as a business venture, he tried to pose as a child in an elementary school in an attempt to trick the principle in to donating school funds to his power plant. It's true he had more realistic and grounded evil too like trying to cancel all the plant employees' dental plans, but in the same episode he does zany wacky stuff with a 1000 monkeys at a 1000 typewriters writing the world's greatest novel and you tend to forget he's evil because that's just so funny. In fact his hilarious ways of spending his ill gotten wealth or his old-timey antics are so cooky and eccentric it's kind of hard to hold on to resentment that he has undeserved power and privilege and besides, again, it's a cartoon so there's no actual real harm to be upset about and the tone of the show and his appearance in it never tries to portray that harm in a serious way so you can't really even be so wrapped up in the fiction that the harm even feels real as in other works of fiction.

They have also occasionally humanized him, as a necessary measure for when entire episodes have revolved around him so he has his troubled past with his lost toy BoBo and his own quick abandonment of his own parents, he's been unlucky in love and he's insecure about his baldness even showing genuine empathy towards Homer for his desperate attempts to use the company medical insurance for hair replacement medicine. In fact I think the few times they really show him as an actual unlikeable prick are when he stays at the Simpson home and behaves like a monster and the time he tried to marry Marge's Mum and was extremely hasty and controlling about it. In both those instances we could genuinely hate him, but they more or less redeem him by having him be forced to accept consequences for the behaviour.