Why does articles sometimes contain [sic]?

The reason you sometimes see [sic] in articles, is to indicate this is how it was originally written and it's often used to indicate there's a grammar error in the quoted text and the one quoting the text, didn't make the error

[sic] can be written without the brackets, but it's most commonly written with the brackets to indicate it's not part of the original sentence and it's also commonly written in incursive

As you can see in this quote example, there's a couple of spelling errors from the referenced text and by adding [sic] you know that's how it was originally written and not a mistake by the one referencing it

Origin of [sic]

sic first started seeing modern usage in the mid-twentieth century and in the beginning it was used a lot in state-court opinions. Then later it's bracket form started to be used in quoted and reprinted material, to indicate this is how the text originally was