It’s to let you see what the replies are and indicate that there are replies, just like where the reply is, there is a link to the post that it’s a reply to.
I had a community that struggled with this duplicated replies issue, which took me quite a while to understand just what they were talking about. Eventually they got used to it, or so it seems.
It is definitely a feature that people coming from other forums find confusing.
And if you do want to hide the replies button, you can do it with CSS. It might be a good idea since people find it confusing. You might be able to come up with some words to use instead of “replies”, like “show the replies that are shown further down below”, but figure out how to say that in 2 or 3 words. 