Why my brother treats my step dad differently than my fiance?

So my step dad can be a jerk. He caused a lot of problems and my brother even almost fought him. My brother treats him with more respect than my fiance. My fiance never did anything to him. We broke up in the past but got back together. My brother tells me how much he dislikes him. I'm like you don't say that about our step dad and he's been around for 3 years. My fiance has been around for 7. I guess he just has a personal dislike for him.
Why my brother treats my step dad differently than my fiance?
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