Spoiler
I think that the reason they made Steve a more likable character now is that he had started to grow on them towards the end of season one. Perhaps the creators saw potential there and wanted to explore it.
I like it myself, since I like his relationship with Dustin and how new relationships are developing and being explored in this season. I think it gives the characters more depth, and there's also good reason for it, since they are all united in their knowledge of the Upside Down.
If I recall correctly, I think they wanted a "human villain" as well as a monstrous one this season, hence they decided to make the new dude more of an antagonist (minor though he is).
I actually didn't like any of the teens in the first season --Steven, Jonathan, or Nancy.
However, as we got to know them a little more in the second season, you can see how they have grown.
Is there a reason you dislike Steve so much? He was definitely a jerk, but I thought Jonathan was just as bad with being the creeper that he is.
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