I don't think this is the case. It's simply because of what the sites were built to be. Reddit is what it was supposed to be originally, practically a forum and steemit is a place to blog.
On Reddit you can say all sorts of bullshit stuff, rage, roast someone or whatever. The community is more free and the community there is.. well.. those kinds of people who like to leave roasted comments or share unvaluable opinions.
In Steemit, it has been states here and there that CONTENT MATTERS. Not because it can't be edited, but I think it's just the people in Steemit.. the community here is more mature and people who like to blog and share their opinions in a more mature way, just think more throughly before pitching in a random comment.
Reddit is for everyone. Steemit is too, yes, but have to be honest here, only certain people end up using Steemit actively and those active on Reddit, aren't the Steemit people.